Lost in all the garbage posts, is the real reason for no WR at RB is because that's what was voted on. Any other reason does not matter, whether it's a speed/weight thing or simply because people don't want WR running the ball.
Once 4.6 came and the speed/weight thing supposedly fixed, I lifted the weight requirement for RB. All that is required now is that a ball carrier NOT be listed as a WR.
I'm trying to keep things simple, without policing a bunch of rules, yet keep things fair and give the league what they want. We voted before to not have WR run the ball and our current re-vote shows people still don't want WR to run the ball.