WB is a very director friendly company. Scorsese and Eastwood have done lots of work there, for instance. That's often the standard complaint about WB in these threads, they let directors pitch movies to them, like the Wachowskis pitching V for Vendetta and Snyder pitching 300 and Watchmen, instead of trying to force products into the pipeline.
It probably should be noted though that this really isn't about Spielberg (who has enought clout to win battles with any studio exec) but about Dreamworks which is more than Spielberg. Disney might be out because Dreamworks has an animation division that would have to fight with Pixar and Disney itself for promotion, release dates, etc. Sony, WB, and Fox are more likely because of that. Maybe MGM even.