A good point.
For me the issue is twofold: (1) Singletary gets injured, we are screwed, Moss is inactive some games, Cook is playing like a rookie and has yet to show he can handle a game; (2) Singletary is a FA after this year and likely pricing himself out of Buffalo, so if we can get Singletary a complement that is on a rookie or low cost contract, we have a RB for next year and don't need to burn a pick on a proven back.
I'm also all for interior OL.