Warner Bros. owns DC comics and as a result, own the rights to almost every DC character. A big reason for Marvel's characters being spread out across studios is the financial problems they had a while back. One of the things they did to keep afloat was sell off movie rights. Even big names like Iron Man didn't revert back until about middle of last decade.
So If they wanted, Warner Bros. could have their movie characters in the same universe like Marvel Studios has been doing. But DC Entertainment President Diane Nelson says they will focus on keeping the films separate for thier "great stories and standalone experiences".
Warner Bros. President Jeff Robinov said in an interview last year that a Justice League movie would happen in 2013. However Christain Bale, Ryan Reynolds, and Henry Cavill will not be playing thier respective characters.
Despite what Robinov proclaims however, there has been no progress made towards a Justice League film yet. Unless there's some Hollywood secrecy afoot, I wouldn't expect it until 2014, if even at all.