It makes it easier when you own everything around it, yes. But being on Windows/OSX doesn't make the DRM unbeatable, just more difficult to break. DRM period doesn't work, but that's not going to stop them from wrapping everything they own in it.
Ah, the old enterprise mindset strikes again. If somebody cracks the DRM on Windows, the movie producers have someone to yell at: Microsoft. Then they can make Microsoft fix it, and everyone rolls out new player software that requires the update to work. We've already been through some iterations of this on consoles, too. If somebody takes five minutes to crack the DRM on Linux... now what do the movie studios do? Go yell at Linus? The net effect of that will "an entertained Linus Torvalds" and not much more.
Of course we all "know" that DRM is fundamentally impossible, but there is a qualitative difference between trying to do DRM on a proprietary platform and on an open platform.
