Like I said, Brady has gone after Wes Welker and some of the OLineman.
So... I'm not sure that Brady is doing it to motivate underachievers. I mean, Wes Welker is supposedly the hardest working player on the team.
Brady yelling at Welker is different than him yelling at Butler. Yelling at Welker, the savvy veteran, if he screws up Brady's competitive side gets pissed at him for that play. When he yells at Butler, the second year player, Brady is trying to push and make him a better player.