Since the Steam platform is being used for non-intrusive DRM for physical copies and online distribution, and as far as my knowledge goes GFWL has been confirmed for 360 Controller support only...

...does that mean that Live is out of the picture, and Steam will be used to Handle Achievements and DLC distribution? Or... did I miss it completely?

GFWL is gone entirely. Poof. Steam handles the achievements and DLC, and the game engine itself is where the joypad support comes from.

Oh, the glee I feel in my heart.