When I watch Kawann Short, I am more impressed with his ability to shed 1v1 run blocks than his ability to shed pass blocks. I don't expect Short to be an NFL star, but he could help create negative plays for opposing rushing offenses- and that's actually something we've sorely lacked lately. Brandon Mebane is still pretty good, but he's not living in the backfield like he did in 2007 or 2008. We aren't just lacking a guy that can break into the backfield on passing plays, we need that guy on running plays too.
Run defense was a growing problem for the Seahawks in the 2nd half of the season, and a major problem in the final playoff game. Short isn't a tank against the run like Mebane is, but his ability to create the negative play in the running game is a really nice bonus to go with his pass rush, IMO.