Who are you including in that category apart from Apple? Compatibility with 30-year-old OS features is often considered a worthwhile goal among current UNIX descendants.
> I see very few people complaining that Apple killed the PowerPC line, and XP far predates that.
Is WinXP compatible with x86 and x86-64? Is Win7 not compatible with those? I don't see what point you're making by mentioning CPU architectures. And the 'universal binary' made this switch largely transparent to owners of either CPU.
> many people hold the misapprehension that XP is 'good enough' in some sense
Leaving aside the accuracy of this, surely if it is a misapprehension then it should cause problems only for those people. Instead Microsoft have made it clear that it's a problem for their own profit growth and that those users need to be coerced into upgrading.
But even that's being done in a half-assed way that makes it more of a problem for web developers. Which other Microsoft titles are being developed to be XP-incompatible? Certainly not Office 2010. Aside: backwards compatibility was largely maintained under Mac OS Classic from 1984 to 2001. The break, coming with OS X, was necessary, not contrived.