I always just assumed that was just a case of the more remote/less extreme areas didn't have as many strong challengers or good training spots, so Brock and Misty's pokemon just never got as strong as ones like Sabrina's (as she was in the center of the largest city of challengers), Blaine's (his were trained in a more extreme environment), or Giovanni's (either fought a lot during all his traveling, or they were stolen).<br/><br/>Eventually they did get stronger, as we saw with their Gold/Silver teams, but it took them a bit longer to get to that level.