Definitely expected from Apple but not cool. The latest Windows can run on PCs from 2005...
And how is the user experience on that 2005 pc? Not trying to argue - that's a serious question.
Also, there's a difference that may be unpalatable, but should be acknowledged: MS still mostly makes their money off software (office, Windows). So it's in their interest to sell as many copies of Windows to as many machines as can possibly run it.
Apple, on the other hand, gives away its OS upgrades. They use software to drive their hardware sales. Giving people years of upgrades creates loyal customers... But they are still giving 6-7 years here. There has to be a limit. At some point, they need to make another hardware sale (or else charge for software).
Anyway, as I said before, I think this is an arbitrary list, which should have included lots more 2009 macs, if not 2008s, but I'm also cognizant of the realities of the business model(s) at issue here.