I'm not an MS supporter, but it's true that they can't be held entirely accountable for the DRM push. A lot of that is out of their hands - and I'm sure they don't want to be taken to court yet again.
How so?
Since there are no laws *mandating* DRM on all content, what's there to force them to support any of it? If anything, Microsoft has such a market force with their total domination of desktop OSes, that it's extremely unlikely that they media industry would have said "OK, then we won't release anything that will work on a windows PC anymore".
Maybe it's not entirely microsoft's 'fault', but they sure appear to be a very willing participant in the whole DRM push.