Hmmm...
- x86 16-bit - 16-bit DOS and Windows 3.x
- x86 32-bit - 32-bit Win9x, WinNT, Win2K, WinXP, Vista, Win7, Server (Win7 server drops x86 support)
- x64 64-bit - WinXP, Vista, Win7, Server
- IA64 - WinXP, Server
- PowerPC - WinNT up to 4.0
- Alpha - WinNT up to 4.0
- MIPS - WinNT up to 4.0
- SPARC - development, never released
- Clipper - development, never released
- i860 - development, never released
When Win7 ships this fall, supported systems will be
- x86 - Windows 7 (last release to support 32-bit x86)
- x64 - Windows 7, Windows Server 2008 R2 (Win7 Server)
- IA64 - Windows Server 2008 R2
There is one quite big mistake, there is no x64, it simply does not exist!
However, there is x86 which comes in a couple of flavours like 16 bit, 32 bit and 64 bit. A lot of people still make the mistake to think that the 64 bit version of x86 is a different architecture while it's not (it still has the basic commands and other stuff a 386 for example has, it's still a 32 bit cpu but only with 64 bit extensions; if you dive even further in it's architecture one can see it's part 8 bit, part 16 bit, part 32 bit and part 64 bit

). Officially the 64 bit version of x86 is called x86-64. So the first 2 points should be just 1.
Also Windows XP does not work on IA-64 since you seem to mean Itanium, Itanium is a server platform only and only Windows Server variants work on that platform.
There is a difference when you make a distinction between business use and consumer use. MacOS X is mostly used by consumers. When comparing Windows and MacOS X in that regard Apple has switched architectures while Microsoft stayed on x86. It's a different story when you start looking at business users and server systems in particular (which you can see in the list you provided). I think the person you replied to was just thinking of the consumer.
That's a good point. And don't forget some people are arguing over INTRODUCTION DATES while I'm referring to DISCONTINUATION DATES.
It's a big distinction. If you're selling something like Leopard or a G5, you're expected to support it for a reasonable length of time.
The last G5 was around 3 years ago to this day.
Leopard was sold to many PowerPC users just over a year ago without them knowing it was going to be a dead end $129 purchase.
That's just not right.
The last G5 was the Powermac which was discontinued in august 2006. If you have AppleCare that would mean the support for this particular machine will end august 2009 which is this month and 1 month before Snow Leopard will be released. That's why PowerPC machines are not supported in Snow Leopard and why users can not see they didn't know about the ending support (something called "responsibility" comes to mind...).
Other then that there are several other things you need to consider on both the technical as well as the economical part why it does not make any sense to have Snow Leopard support PowerPC.
First the technical part:
The PowerPC Macs mostly have G4 or earlier PowerPC cpu's in them which are 32 bit single core cpu's. Those machines also have only 1 cpu in them. The Powermacs and the iMac are the only machines with the G5 which was a 64 bit cpu but still with only 1 core. The iMac only had 1 cpu in it but the Powermac had either 1 or 2 of those G5 cpu's in it.
On of the improvements in Snow Leopard has to do with the multithreading/multitasking part of applications and making better use of multicore/multicpu systems, another one has to do with making the system 64 bit with the ability to run 32 bit on top of it (Leopard is the other way around). Therefor it is useless for more then 90% of the PowerPC machines. It's only useable on the Powermacs with 2 G5 cpu's (multicpu and 64 bit).
The other improvement in Snow Leopard has to do with OpenCL. There are not many graphics cards from ATI and Nvidia that are compatible with OpenCL. That's why a some Intel Macs will not be able to use OpenCL and thus take full use of the improvements in Snow Leopard. These machines involve all of the machines with Intel graphics and the unsupported ATI and Nvidia graphics cards (you need to thank ATI & Nvidia for not supporting those!). This won't be causing a lot of problems since not many will be needing the extra power you can get with OpenCL. It's most useful in some specific applications such as rendering software. People running such software most likely use a Mac Pro and those machines are able to support OpenCl with their graphics card (either because they have a graphics card that supports it or because they are able to upgrade to one that can). Not many will have the need for OpenCL (though it's really nice OS X supports it!).
All of the other improvements are very minor and have to do with cleaning up the code and making things more consistent. The last part can be seen visually and can be solved in Leopard as well through the use of skins (there are apps for that). It's not something that is necessary, it won't make the difference as in "the machine works", "the machine doesn't work". They are just nitpicking details they fixed and it's not a major problem if you don't have those features since Leopard works just fine.
So technically there is almost no reason to upgrade to Snow Leopard for anyone, especially PowerPC users have no benefit when upgrading to Snow Leopard. The same reason why a lot of people still stay with their PowerPC machines in the first place

For those people it's ridicilous in the first place to complain they can't upgrade to Snow Leopard. They don't need to, they don't have to because what they have will work just fine, it won't stop working when Snow Leopard is out on the market (they don't use DRM on OS X in that regard).
The economical part:
Apple made the switch to Intel only starting somewhere in june 2006. A lot of people where waiting and wanting Apple to do so. Since the switch to Intel a lot of people switcht to a Mac because it meant that they were able to run all of their x86 stuff AND MacOS X. Apple gained a lot of new users and their sales are still going strong (even better then in the PowerPC age I think).
The other part is that most of the PowerPC machines still in use are either being used by enthusiasts (people who don't mind running the OS it came with) or professionals. In case of the professionals computer systems won't last longer then 3 years because after that period those machines become more expensive. In those 3 years things also have evolved. In case of Apple it has evolved a lot in computing power since the switch to Intel (a Mac mini from 2007/2008 is able to outrun a Powermac G5 with SMP). Those people need the computing power so it's very likely that they've already upgraded to the Mac Pro at some time.
Then we have the software problem. Most developers have turned to Intel only since most of their users or even all of their users use Intel Macs. The amount of new version still having PowerPC support is still dropping. This makes the PowerPC Macs less attractive to use nowadays. Doesn't mean you can't use them anymore or that they are useless, they still work with all the software people already had, just not with any recent version.
Add all this up with the fact that the AppleCare support of the latest PowerPC machines will end this month (august 2009) before the release of Snow Leopard and you'll see that from a economical point of view there is no reason why Apple would support PowerPC.
All in all it's sad to see the support for PowerPC Macs go as they are fine machines to use even if they're old. But on both the technical and economical part there aren't any reasons why they should still support PowerPC and why you as a user would want Snow Leopard. It's a small upgrade and that's why it costs 29$ instead of the regular 129$.
And at the end of this lengthy post we come to the ontopic part: 10.5.8 works nicely on my 3 Macs. I can't really see much improvement regarding bluetooth, it still takes some time for my bluetooth keyboard to start working, the wireless mighty mouse is instant though. Same goes for the AFP fixes (smb simply works as it should, AFP keeps complaining about not having the proper rights).
I'm also curious about why system profiler reports the hardware UUID, bit odd.