An interesting piece of Battlefield 3 information popped up overnight, it appears that the game might be headed to Steam after all is said and done. Either that, or an EA account representative is extremely mis-informed. According to a Redditor, they had a conversation with a representative from Electronic Arts where they were told that the game would be available on Steam…post launch.
This means that after the initial releases are filled which means launch day buyers, pre-order pick-ups, etc ,the game will be available on the Steam download service. The representative didn’t go into details regarding how long this period would be, but EA has worked out multiple deals with every other digital distribution channel to secure launch day availability. If you must have it on Steam, and you don’t mind waiting, it appears that you may be in luck.
Source: Reddit