In actuallity, this discussion goes back much further then that. When he was traded to begin with, I remember having the same discussions about him in Gibbs' offense. Gibbs uses his backs in a very physical style of offense. It's hard to stay healthy if your a big back, much less a smaller back. If you look at Portis from the time he came into the league to now, one thing will jump out at you immediatly. He averaged 282 carries per season in the first two years (at Denver). His AYPC was 5.5. While in Washington, (prior to last season when he was injured for half the year), he has averaged 348 carries per season. His AYPC has dropped to 4.06 since he's been in Washington. That's a major difference in production. Basically, he had fewer carries and more yards per season while in Denver then he has had in Washington.
He's not long for the Show IMO.