I think the difference in software support has to do with Apple always pushing forward at the expense of the past, while Microsoft tends more toward backwards-compatibility.
The problem with this is your still-working-fine Apple hardware gets left behind.
Apple also has the walled-garden philosophy (an ecosystem where their hardware and software work together well), while Microsoft's Windows has to somehow work in the Wild West of hardware from anybody and everybody.
FWIW, rumor has it a new Mac Pro is coming, but I am personally not in the market for one or anything else for that matter, because I already have an ugly Mac/PC and a wet Mac ;-).