@onemoreposter: what mutant is physically stronger than colossus? The only characters I can give that to are namor and apocalypse if he enhances his strength. I dont think The thing has ever been stronger. Colossus was much stronger when he first got his powers than the thing was. Due to natural mutation and excercise they would both get stronger; but colossos has a much higher strength initially.
Your right about the movies though. Everyone knows he is capable of more.
Colossus is also a part of a team with several branches and dozens of members. Its hard to show what someone is capable of when there are so many other characters to work with. Ben on the other hand is the strong guy in a team of 4 so his strength will always be displayed and capitalized on.