I mentioned Steve Jobs' open letter about DRM a week or so ago. Of course it's not quite that clear. Bruce Schneier with some thoughts on why software companies such as Apple or Microsoft might really want to use a proprietary DRM system:

This isn't even about Microsoft satisfying its Hollywood customers at the expense of those of us paying for the privilege of using Vista. This is about the overwhelming majority of honest users and who owns the distribution channels to them. And while it may have started as a partnership, in the end Microsoft is going to end up locking the movie companies into selling content in its proprietary formats.

We saw this trick before; Apple pulled it on the recording industry. First iTunes worked in partnership with the major record labels to distribute content, but soon Warner Music's CEO Edgar Bronfman Jr. found that he wasn't able to dictate a pricing model to Steve Jobs. The same thing will happen here; after Vista is firmly entrenched in the marketplace, Sony's Howard Stringer won't be able to dictate pricing or terms to Bill Gates. This is a war for 21st-century movie distribution and, when the dust settles, Hollywood won't know what hit them.