Your not "left dangling." All you have to do is buy/obtain an XP install disc, and install it on your PC that came with Vista. There is no technical reason you can't do this. Apple on the other hand has made it basically impossible to Downgrade newer Intel macs to Tiger. (Not that Im complaining since I love Leopard) Just making a point
Sort of. This is NOTHING like the 68040 days or the PowerPC days of 604 and 604e. Back then there really was almost NO way to install system software older then the machine. Anyone recall all those enablers?
But this is less how "Apple is" and more what "Apple does". There have been some MAJOR changes in the Mac platform's hardware. To ensure compatibility there was often a system update accompanying any new hardware, or an enabler. Its all about how tightly Apple integrates the software and hardware. This has also allowed much more control and thus an evolution. This also gives the most "optimized" performance. This is either good or bad depending on how you look at it.
My TiBook from 2002 runs Leopard fine, I also run iPhoto and most any current software from Adobe or Quark just fine. If this was a PC there would be no way to run Vista. But at the same time its a G4, so I get no photo-booth effects and a few other things.
Since the transition to Intel, this integration has loosened a lot, really since OS X even.
So I see no problem with buy a new Mac today and being able to install Tiger. It should go right on until there is a major hardware change.
I am happy with the way Apple has evolved the platform. I still laugh at PCs that come with floppy drives and parallel ports. There has been little evolution on the PC side, just optimizations. At the core, a PC is little different than one from 1990. A Mac on the other had has nothing in common with one from 1990.