I'm going to paraphrase two posts I read on Destructoid yesterday that sum this up nicely:
Why in the world did they pick GFWL? GFWL live is just plain broken and it will actively discourage people from playing it. Steam works better, has a better reputation, and it will get all sorts of free advertising on the front page. This decision is baffling.
DRM is like taking a shit, nobody really likes it but we have to deal with it. However, Steam would be like a normal healthy BM that leaves you feeling relieved and you can get on with your life; where as GFWL is a gigantic, bloated, painful kind of constipation, the kind where you sometimes can't even finish, or in this case buy/access you games/saves.