That is an artificial obstacle that Apple implemented to force people who purchased expensive computers to buy new ones.
The original 2006 Mac Pro is a 64-BIT computer. And it is capable of running the newer OS X versions. Apple just blocks the installers from running on those machines.
It's all about artificially obsoleting their devices to force new purchased. Often, it just sends people back to Windows.
I can't use iOS 9 on my phone either. Because the latest iTunes I can install on my machine is 12.2. Guess what Apple, I'm not buying another mac. And since iOS 9 requires a newer version of iTunes, they also just lost future phone purchases from me.
Greed can be your own undoing sometimes.
An example of good product support is Microsoft. My 2006 Mac Pro does have Windows 10 64-BIT installed and running natively without any boot camp software involved. I just installed windows 10 on a separate hard drive and booted right up.
Windows 10 is also running on machines as much as 10 years old or older. That is support.
That's is one way to spin it.
I seriously doubt Microsoft tested Windows 10 on a 2006 Mac Pro to ensure that it'll run. If it happens to run, wonderful. If it doesn't, Microsoft made no promises. That's not support, that's luck of the draw.
Microsoft has to produce something that will run on any PC clone (which is no easy job). You want to know if your PC will support various Win 10 features? Read the
system requirements pages, and figure out for yourself whether your machine makes the grade. That has nothing to do with "support" from Microsoft, it's a question of whether your hardware will support what Microsoft has produced. The list of deprecated features for Win 10 is pretty long and complex. If you have the tech ability to wade through it, no problem. If you don't, every one of those is a potential gotcha - one or more advertised features that will not work after you've gone to the trouble of installing it.
Meantime, Apple has the luxury of producing an OS for a limited number of models, and knows, feature-by-feature, exactly what models will or will not support them. Although
Apple's list of Yosemite's deprecated features isn't all that short, anyone who knows the model(s) they own will see, explicitly, whether their machine supports that feature. That's a different kind of support, but support it certainly is.
Here's a question for the conspiracy theorists out there. Mountain Lion (10.8.x) required an early 2008 Mac Pro (or newer). Mavericks (10.9.x) ran on an Early 2008 Mac Pro (or newer). Yosemite requires an early 2008 Mac Pro (or newer). El Capitan runs on...
every machine capable of running Yosemite. So, if Apple was hell-bent on artificial obsolescence, don't you think those early 2008 Mac Pros, mid-2007 iMacs, mid/late 2007 MBPs, late 2008 Aluminum MacBooks and MBAs... would have been dropped from the list by now?
And it's a shame if Apple's nefarious behavior "just sends people back to Windows." Considering that Apple is the only PC-maker that has been regularly increasing market share over the past few years, imagine how much larger Apple's share could be! Instead of selling more than four times as many Macs in 2014 as they had in 2006, it could have been five times, six, seven times as many.