I think it only seems that way because the open-source world has worked much harder to break into that garden. Apple put a .mp4 gate around your music library. Microsoft put a .doc gate around your business correspondence. And that's before we get to the Mono debacle or the EEE paradigm.
Microsoft is a better corporate citizen now because untold legions of keyboard warriors have stayed up nights reverse-engineering and monkeypatching (and sometimes litigating) to break out of their walls than against anyone else. But that history isn't so easily forgotten.