But what's being pointed out is that Superman Returns
didn't fail on it's own merit. Before a dime was actually spent towards the movie, it was already carrying about a $150Million burden from previous false starts. If it wasn't burdened with that previously spent budget, it would have performed a slight bit better than Batman Begins.
It was front loaded to fail
And I remember at the time when BB was released, there was kind of a perception in the media that it had under-performed at the box office, when compared to the mega-bucks that Batman or Batman Forever had raked in. You had an actor who wasn't that big a draw in the lead, surrounded by character actors - there was no stand-out superstar like Nicholson or Carrey playing a well-known villain (Ras and Scarecrow didn't have the same recognition value as Joker or Riddler).
The main difference between SR and BB - apart from the fact that BB wasn't saddled with the budgets for all the previous attempts to get a Batman movie off the ground - was that the latter seemed to enjoy a more positive response among fans and, perhaps more importantly, sold better on DVD, thus building up demand for a sequel. I personally like Returns a lot but I wasn't overly anxious to see what happened next in that universe, whereas I couldn't wait to see what Nolan and Bale's Batman did next.