I think this is going to be the next big debate in NFL statistics/gameplanning. The problem is that even the worst passing teams average as much/more yards per pass attempt than the best rushing teams average per rush. A team like the Panthers is only averaging 4.2 NY/A passing, but they're also only 3.8 YPC rushing.
You do absolutely need to be able and willing to run the ball, but I think right now it's hard for teams to figure out the right balance between the inherent inefficiency of running the ball with the need to keep the defensive line honest.
It's hard to summarize it briefly, but yeah, it has to do with either following all the way across (usually means man, or at least some form of man), or watching the way they shift to hopefully learn something about the zone they're playing.
How to handle motion while still disguising coverage is just another move in the game of chess for the defense.