I knew IM3 would increase from the previous one but I never saw it increasing by that much.
$400M (an increase of almost $100M from the previous one) is pretty darn impressive. Not to mention that massive WW gross of around $1.2bn. I can't really say I'm too bothered by its legs because it faced some pretty hefty competition (Star Trek, FF6, GG, TH3 would do damage to virtually any movie) that would always have cut into its legs (I mean, RDJ is popular but this is Iron Man we're talking about...not Batman or Spider-man).
Iron Man isn't Spider-man, Superman or Batman, for Marvel to have built up the character to that level, much credit must be given to them.