When Electronic Arts decided to heavily push its Origin web portal and distribution service at E3, alongside word it would be the exclusive home to Star Wars: The Old Republic, it became an open question whether EA would continue to play ball with Steam. We appear to have an answer to that question, with Crysis 2, Alice: Madness Returns and Battlefield 3 all disappearing.
So far, I've been unable to get an answer from any party involved. Valve, EA and Crytek have all, to date, remained unresponsive. Other outlets are reporting a statement's coming later today.
You can still, however, purchase other EA games on Steam. Crysis and Need for Speed are still there, as is the Need for Speed series. It mostly seems that EA's chosen to start holding back its most recent and upcoming releases, in hopes of driving consumer traffic to its own service.
As soon as I know more, I'll pass it on.