An interesting idea, to be sure. It's not like Blizzard necessarily needs help from Microsoft to promote and develop their games -- if anything, it's Microsoft that could probably take a lesson from Blizzard on how to release software. But it's true that console innovations like achievement points and Xbox Live social networking accounts aren't really finding a solid place in the PC gaming world, and it could be that Blizzard wants to see those types of things on the platform.
Blizzard has always had a rocky relationship with consoles anyway, and the recent announcement of a non-console Diablo 3 definitely shows they're interested in the PC (including Mac) platform only. Can't really blame them for wanting a little more love from an OS developer like Microsoft.