The DRM is actually implemented for Moonlight already, it's just distributed under a closed and exclusive license. Microsoft disseminates these relatively freely to embedded devices, but refuses to authorize the use of that component on desktop Linux because they are concerned that doing so would increase the likelihood of a crack for their DRM.
I guess their thinking is that the technically inclined use Linux, and if a Linux desktop client exists, someone will get bored one day and reverse-engineer the DRM. As it stands, you have to have significantly more determination than that to crack the DRM from Boxee, and it appears that nobody in the community has that determination since we have not seen a crack or reverse implementation.
