The differences between Marvel Studios and this proposal for a DC Studio are firstly Marvel Studios have had successes under their belt even before the Disney acquisition, such as Iron Man, so I think Disney is content to leave them as autonomous company under their wings for future film development. Also, Disney perceives Marvel very different than how WB sees DC, because Disney wanted to branch out to the young men demographics (because Disney's brand already has the children and young girls' markets cornered), so they want Marvel to "do their things" because Disney doesn't have alot of experiences attracting guys to their products.
On the other hand, WB pretty much treats DC as just another unit in their company, and they haven't spent alot of attention or resources to try to maximize the DC brand. DC superhero movies have had to obey WB's business plan of having only a handful of tentpole films a year, so except for Nolan's Batman trilogy WB hasn't bothered to make many movies under the superhero genre. The few times that they had, they were disappointed with the results (Catwoman, Superman Returns, and the recent Green Lantern for instance). Plus, the creation of the DC Entertainment unit was basically a joke, because they are just a consulting unit and have no input on DC's biggest property, the Batman franchise.
I think after MOS has concluded, aside from a Batman reboot there's no guarantee that WB would bother to make more superhero movies, except for maybe JL but that depends on the success of The Avengers and their perception of that success. JL could be a safer gamble than doing other solo movies, because if it makes alot of money WB can use it as a launching pad for other projects, such as WW and Flash. If it doesn't, then WB can just shelf it like they do with other movies that sank to oblivion.