Battlefield 3 could still arrive on Steam in time for its release on October 25.
The EA and DICE shooter isn't on the Valve digital distribution platform currently because the two publishers involved couldn't agree on terms regarding the release of DLC.

EA issued a frank statement back in August explaining the situation but gave some hope by saying, "We hope to work out an agreement where Steam can carry Battlefield 3."

According to a report on Battlefield 3 Blog from an 'anonymous source at Valve' those negotiations are still ongoing but the two sides are "very close to reaching an agreement regarding the sales of DLC content."

http://www.computerandvideogames.com...-steam-report/