Personally my training still includes a large element of speed work (2/5 sessions) and I may not be the fastest, but I'm reasonable (top 25% in most races). Once you have built up a reasonable fitness and distance base then speed is the next thing to work on. i can't imagine that any of the sub 13hr boys and girls just do long and slow miles. i'm quite sure that any of them would fair well in much shorter races.
eg Top Novice Konrad Rawlik