You often see these really large heroes in scifi/fantasy that really tip the scales. Somehow they are able to sit in chairs and ride around in normal vehicles. I think even the stairs and floor would be a problem for guys like the Thing or Colossus. Sometimes they show a guy being a little heavy and it having some effect, but it is mostly ignored. The Thing in the elevator, Wolverine on the motorcycle, and the Terminator in the awful Terminator 3 are a few examples of the writers actually acknowledging the character's immense weight.
