Besides, if the only place to get a particular song were at iTunes then the argument might have merit. But the vast majority of the songs are available elsewhere, if not online, then on CD. So as Paddy says, buy them someplace else.
And as D76 suggests, if this is to be taken any further we will soon see all software being forced to be compatible with all OSes...no such thing as proprietary anything anymore. And while that may initially sound good, it would be a major blow to capitalistic ventures everywhere. Lacking altruistic motives, much of present day innovation would not exist.
This sounds more like the Open Source community behind the move more than MicroSoft.
However if taken to it's logical conclusion this would allow Microsoft to prevent other OS's from interacting with Windows.