Bush is not really a running back. Bush's heroics at USC overshadowed this, but in his last two years at USC, Bush only carried the ball 343 times. His teammate LenDale White had 400 carries. Even if you count receptions, White still had more offensive touches than Bush did.
In the epic 2006 Rose Bowl against Texas, when USC went for it on fourth-and-two from the Texas 45 to try to seal a win, Bush wasn't even on the field. White got ball (and only got a yard). In the game, White ran the ball 20 times and Bush only ran it 13.
Sports reporters make big deals about small differences in numbers. USC played about 24 games over those 2 years so the average number of carries for Bush and White are 14 and 17. So White carried the ball an average of once more a quarter for 3/4s of the game than Bush. I'd still call Reggie Bush a running back.
And in the second paragraph we see how sports reporters love to generalize over a single game (or even moment). If a guy carries the ball 13 times during a game then he is a running back. He might be second string, but he is still a running back.
