I have noticed this. It seems to me weak side runs work better because the blocking is better on the strong side. By which i mean the edge rusher is not constantly getting you from behind. The edge rusher on the weak side constantly blows up plays from behind when running to the strong side. For some reason the game is programed to make edge rushers the best run defenders as they just explode running at 1.2 40 speed around your end lineman. Sometimes it is the end, sometimes an olb and sometimes is a safety. Everytime i see a safety come down on a blitz to the opposite side i am running to i know i am screwed.