This is an important lesson. I am personally not a fan of the Windows programming model* and I despair the number of security holes over the years, but I am quite aware that a large part of it stems from Microsoft's commitment to extreme backwards compatibility (which I also recognize has sometimes taken heroic measures).

I'm actually surprised how long Apple takes to obsolete APIs (carbon lingered forever) and how far back they are willing to support old hardware. They project an insouciance towards old APIs but tend to give a lot of advanced warning (e.g. the obsolescence of 32-bit applications was announced at least five years ago). They seem to be far less conservative towards UI, and prefer to rewrite rather than update which leads to a bunch of new bugs. That might be what gives people the impression that they junk APIs quickly.

* that's a matter of personal taste, not meant to start a flame session.