To me Marvel have always done something that DC havent, and that is not making films about stand alone Graphic Novels/Stories for instance Jonah Hex, Constantine, V For Vendetta etc, they are all stand alone I dont think you will see Batman in V for Vendetta some how, do you?
Where as Marvel have made films about characters that can intertwine and essentially made the films they have to lead up to Avengers which is a smart move. As well as that Marvel pick characters with ALOT to draw from where as if DC only has say V for Vendetta then all they have to draw from is that one piece of resource which is the Graphic Novel.
If DC keep doing stand alone features then that is it for them, If they are now looking to do a JL film they need to stop making films like Joah Hex and concentrate solely on different characters that are able who actually have connections with other characters so they can make a little guest appearance in other characters films (like Wonder Woman could appear in Superman, if only for a few minutes then that could wet the appetite for fans wanting a Wonder Woman film)
Also ATM I dont think it would work if they wanted to do a JL film (which i am thinking they will because of the success of The Avengers). They need nay MUST get all the people who have stared as them in the solo films I.E Christian Bale etc. as then you have some continuity which the whole franchise. I'm sorry I am not going to see a JL film where they recast the entier cast. That is one of the reasons why The Avengers did so well same actors and we felt like we knew the characters.