True, but their have been times in the comics when Spiderman tried to profit from his crime fighting. I remember at one point he asked to join the F4 because he thought it would be a paying job. Also, he's reported crimes as a civilian in hopes of collecting the police reward.
The reason I find Spiderman selfish (mostly in his film incarnation) is that he constantly is bemoaning how he can't have what he wants in life. In fact, he abandoned the hero thing in Spiderman 2 so that he could have what he wanted in life. Iron Man and Batman may be rich, but their mono-maniacal dedication to their ideals keeps them from ever having real relationships, friends, etc. Batman is the epitome of personal sacrifice. He may have money, but that does not mean in any way that he's happy. In fact, Batman has pretty much accepted that his life is not going to be happy because he feels that until he wins his war on crime and injustice, nothing else matters. Struggling isn't the same as sacrificing. Batman and Iron Man sacrifice pretty much any chance at being happy and having a normal social or romantic life in favor of dedicating themselves fully to their causes. They also don't whine about it. They accept it. Again, this for me is what kills Spiderman. He whines constantly. I don't care how broke he is or how strained his romantic life is, he whines. Plus, he's always implying that he needs something more out of life. A girlfriend, money, a father figure, etc, etc etc etc. The list never ends. Spiderman may be a hero, but he never fails to find something wrong with his personal life. Batman and Iron Man have problems in their personal lives too, but they don't whine about it all the damn time. I think the movies really just killed Spiderman for me because as noble as his intentions may be, and as much as he thinks he's dedicating himself to the cause, he never seems to be satisfied with anything in his personal life, and always finds some way of making his problems more important than everyone else. That, to me, is the epitome of selfishness. Perhaps he's a little bit less emo and selfish in the comics, but if we're talking about films, Spiderman is extremely self-centered in all three films. Stark may be a prick sometimes, but he never loses sight of the greater good.