Ah, I see. I rarely buy movies on disc and never pay attention to the digital copies, so I didn't realize they included both.
The DRM issue isn't as cut and dry as you might think. It's not really a simple dumb omission as a complicated story of tech history and old Microsoft technology ("old" like 2003.) Microsoft has changed around its DRM several times. When the old system was in is height ("PlaysForSure"), there were no pervasive online Microsoft accounts of any kind, so there
was no
identity to tie it to. It also wasn't agiven that a computer would have a regular Internet connection to enforce identity, or verify ownership when files were moved. So DRM was pretty solidly anchored to your PC and rights where handed out to devices when they sync'd via Windows Media Player (depending on the rights rules, obviously.) You absolutely could (and can) move the files to other computers, but you have to do it within specific scenarios and under certain limits. Those annoyances were commonplace in all DRM and a big part of the backlash against it.
Microsoft has long since moved onto a new DRM system, used in Zune and Xbox, and that system is tied to your Microsoft account and very portable. New non-PC devices like Windows RT and Windows Phones do not support the old DRM system. But Microsoft, being Microsoft, can't unilaterally ditch support for the old system. Old media players (remember Rio? Archos?), Windows XP, etc etc still use it, and so obviously do the movie studios. Microsoft will need to work with studios to get them to include WMVs that use Zune/Xbox-store DRM. (How possible that is, I have no idea. You can buy movies from Zune/Xbox and I don't see why the studios can't provide a file that uses that DRM, but how it would get provisioned to your Microsoft account, etc, I dunno. Also, MS might not have the clout to get them to do that, since the Zune/Xbox system is much more tightly under Microsoft's control. In the old system, the studios can create that DRM without Microsoft's involvement at all.)
Edit: oh, yeah, what J515OP said.