I don't disagree that I'd rather see Greg Bryant on the field rather than Chris Brown and maybe others, especially if they're running jet sweeps (never give CB the ball again on that, please), but there is something to be said for having a backup at a position.
If you simply put Bryant on the field you're left (or were) left with McDaniel as the only option at RB if Folston needs a breather or gets dinged.
I think you have to consider that practice reps/etc. come into play on decisions like this, and if I'm correct Bryant actually got a couple carries on jet sweeps on Tuesday (is my memory correct on that?), which shows that with more time to prepare and no game the next week you can do more with the depth chart.