I think Step scores are also used to determine fitness for passing GI boards (as well as IM boards-- no PD wants to take someone in danger of failing IM boards and deal with it during fellowship). Failing or showing poor performance any Step (including II and III) is a red flag that one would need much work to overcome.
Just goes to show, dont listen to all those people who tell you Step II and III don't matter. In my opinion, you don't need to rock them, but don't blow them off. Also, don't forget, ERAS for fellowship asked for my Dean's Letter (not sure if any programs actually looked at it, but they all downloaded it).
I agree with above posters, in that other things in your application matter far more than the Step scores (where you do residency, LOR, research, etc).