The support library allows you to use features of newer system releases on older systems. See also GDI+ for Win98/NT4 or Windows feature packs for example.
The API changing game is another problem - it does not allow you to use existing application with newer system. As far as I know, this does not happen on Android (for now).
As anyone noticed how many MacOS X APIs have been deprecated since the early days?
Or the API changes in Android?
Every corporation plays this game, as you point out.
I still remember the early COM days, where the only API was C based, and COM was called OLE.