What about them? First of all, forget about BenJarvus Green-Ellis. Secondly, nobody can effectively utilize FIVE running backs in a single season. Usually you have a featured back that shares the load with a second guy...maybe a third guy will make some kind of impact, but four is stretching it hugely. Running back by committee only goes so far. It usually won't last either because, if you have two guys that should be the featured back, one of them is bound to go to a different team very soon.
The first thing you have to ask yourself is who your featured back?
So, I ask the question: who is New England's featured back? The only running back on your team that has ever even broken 1,000 yards in his career hasn't even played a down for you yet...of course, that's Fred Taylor, and he's 33 years old and going into his 12th season. Obviously, you picked up Taylor for a reason...maybe not to be the featured back, but then again, you haven't had one of those in a while. On the other hand, New England has got it done without great WRs either.
Also, the running backs in New England look better than they really are because the rest of the offense is so good IMO. You can't tell me they don't benefit from that. Granted, Faulk can catch the ball, and Morris is underrated, especially considering that not everybody knows who he even is, but they have been on a good team.
Imagine how the RBs from the other teams in the division would do on the Patriots team. All the other teams have a decent 1,2 punch in worse offenses.