Wing players have the ball in their hands, rules at their side, while they can slack off every now and then at the defensive end. But, big men, especially capable centers, they have to play both ways, facing the most banging and abuse, protect the paint, and come out to help at PnR.
That's why I alway appreciate great 2-way big men more. That's also why I chose Dream over MJ to root for when I first became a NBA fan.