The way it's been explained to me:
All things being equal, board scores will influence the decision. However, all things are never equal, so attitude, personality, letters, research, etc will come into play.
I'm sure every program has a Step I cutoff at which other factors far outweigh board scores. Whether that number be 220, 230, 240, or 250 depends on the program, but I think each program has such a number. If I were a program director I would rather choose someone with a lower score but better attitude than someone with a higher score and difficult attitude. Someone who gets a 240 can handle the material just as well as someone with a 250, and since there isn't a difference there they might as well emphasize other factors that will affect success at their program.