I think the Apple use case has now come down to "If this appliance in the configuration you buy today meets your needs now, and for up to the 3 years that the AppleCare lasts, you're golden. If not, well, OS X may not be for you."

Frexample, I'm looking at what's coming down the gaming pipe, and I'm seeing games that (thanks to the PS4 and XB1's unified memory models, and the tendency of developers to write stuff with consoles in mind) have a requirement for 4GB of VRAM. This is inconvenient, but I can go out and buy an NVidia GTX 970, sell the GTX 660 on eBay, and carry on happily.

Anything other than casual gaming on a Mac? Busted flush in the next 2 years. Even mildly graphically demanding games that would otherwise be fine will run like dogshit because of the differing memory model.