.Mac. said:
In ESB, with Hamill's injury to the face from a car accident, they implemented that injury into the movie by having the Wampa swipe at his face. That actually worked out very well and added realism.
The wampa attack doesn't actually explain Luke's different nose between the first two movies. You look closely enough, and it's easy to see that Luke has Hamill's post-accident nose even before the wampa slaps him across the face.