Superman wouldnt top superman returns if that was how the schedule worked out. Superman cannot open in the same month as the Hobbit. It will be 2006 all over again. Superman will get completely drowned out and passed over for the bigger franchise opening around the same time. Superman can handle Star Trek 2 (which I see being more Iron Man 2 than Transformer 2 in terms of increase over the original film); it cannot handle the Hobbit. Open within 3 weeks of the Hobbit and Supermans potential cut in half. The Hobbit will be getting the (vast) majority of press buzz and will be the dominate movie discussed by the public for any month that it opens. This is devastating to Superman.
Why can't W.B. open the Hobbit in the summer? Stick The Hobbit 1 in July 2013, and it will challenge every record TDKR will set next summer. It's worldwide gross will be the roughly the same. Superman, on the other hand, cannot be released on 2013. That fact alone means Superman should be getting the December 2012 precedent.
Neither movie should be opening in November (Bond and Twilight will severely limit its overseas potential). W.B. should give Superman 12/19/2012 and Hobbit mid July 2013 and 2014. That is the best business decision they could make.