I must have missed this the first time around, but I found a link for the story at RotoWorld.com tonight. It's ProFootballFocus.com's rankings of the NFL RB's pass blocking skills, and the Panthers did not score well. DeAngelo Williams ranked 34th, and Jonathan Stewart ranked 37th, out of only 41 RB's rated.
Here is the formula used by ProFootballFocus.com to calculate 41 NFL RB's pass blocking efficiency.
PBR = (1 - ((sacks + 0.75 (hits + hurries)/pass blocking snaps) 100
Jonathan Stweart = (1 - ((1 sack + 0.75 (1 hit + 10 hurries)/ 96 pass blocking snaps) 100 = 90.4%
DeAngelo Williams had 57 pass blocking snaps, 5 total pressures allowed, for a 92.5% pass blocking efficiency rating.
Newcomer RB/FB Mike Tolbert wasn't among the players listed, so maybe that's another reason he was signed as a free agent.