Superman Returns underperformed relative to its budget, but it wasn't an outright flop.
Maybe it wasn't the worst flop in history but it was still a flop. Box Office Mojo gives it's budget at US$270m and it's worldwide takings at US$391.1m. Yes it might not be accurate but a rule of thumb is that a film has to make at least twice it's budget to turn a profit. so there was a short fall of some US$149m.
But in the case of Superman Returns I thin I remember reading that some of the costs of the aborted Superman films were added into that Budget. So without those it might have turned a small profit.
Agreed on all points.
Even still, it almost brought in enough ( maybe not "made" because of it's huge budget and the older projects being attached to that budget) that the studio would consider greenlighting a sequel.
In this case WB did the wise thing, at least financially. Just in terms of the money it brought in,
Returns was a bigger hit than
Batman Begins, but they gave the green light to a
Batman sequel then to
Returns, because (I believe) WB knew that it was about more than just the monetary figures.
Batman Begins brought in less, but people talked about it more. They were stoked. That enthusiasm wasn't prevalent among people walking out of
Superman Returns. Sure, many people liked it, but their weren't tap dancing out of the theater, and they weren't really talking about it. Not really.
I believe the best, single "business" decision Nolan has ever made (and it probably cost him less than a dollar

) was to put in the "calling card" scene at the end of
Batman Begins. It got people stoked more than anything else; they just got a great origin story, a new, grittier take on Batman, a take that was more realistic, and now there was the promise that Nolan would bring that vision to the Joker. Unlike the reaction of people walking out of
Superman Returns, people were stoked, completely psyched about the possibilities of the sequel.