This is a condensed version of a longer tutorial by Alex Gibbs that you can purchase at Coaches Choice, but his basic explanations shed a lot of light on what the Seahawks do in their run game. Gibbs was a mentor to Tom Cable and Cable still adheres to a lot of the main principles of Gibbs' system.
He talks about "cutbacks" vs. simply running straight up the field or bouncing it outside:
"The cutbacks are geared based on the aiming spots of what is happening up here (points to defensive line). I don't call that (indicates a run straight up the field) a cutback.