Because it has to be shoulder to shoulder and even then if it is too 'robust' a lot of refs give a foul.
Have to ask, were you at the game? How was is a push in the back not a penalty. Granted, there were a few decisions that were wrong, Upson penalty shout, push on Brezovan.
Have to say I didn't see it that clearly from the south end of WSU but if anyone has seen the replay on the telly I can't see how you can suggest it wasn't a penalty. Barnes is goal side of the defender and ready to head towards goal when Morgan clatters through the back of him. It's not even...