Well that's a tad selfish. Let him do what he wants. It's his.
I would suggest swaying away from the "it's excessive" argument. You've got a MP and an iPhone 5, too. And you're trying to get a free iPad because your MBP is too heavy.
But hey, whatever makes you two happy.
Well I can't really use my Macbook in class as it doesn't even hold a charge for a whole class. I paid for my own and his iPhone and I've bought him a bunch of clothes and food this past month because my parents don't really have money. Also, he admitted he wasn't going to do anything productive on it so might as well give it to his older sister who will be doing something productive with it. Because I'm tight on money (partially because of him), I just think it's probably not the best idea for my brother to have an iPad just to play games. If I could afford to buy an iPad or a new computer myself, I definitely would.
Yes, it is selfish, but I've definitely spent more on him than a whole iPad is worth.
Edit: He also is a slacker, so I worry that giving him more reasons not to focus on schoolwork will result in him having bad grades. He says he wants to be a doctor, so that's not really an option if he wants to succeed.