Why would the game files have to be handled by Origin?
As was said, I'd imagine that it'll be more like GFWL with two distinct parts. A client that handles downloads of games bought within it, and a game client/overlay that just runs separately with the game that supports the friends list and cross game chat + the like.
I'm just picturing a steamworks style thing where you have to have the game linked into Origin so no matter where you buy the game, it'll have to be tied to Origin, I think EA will be too keen to force the software on as many people as possible.