Absolutely wrong.

These kind of deals are meant to help assuage any guilt you might feel for spending money on a worthless virtual item that you don't even get to own. It's a marketing tool designed to convince people sitting on the fence to go ahead and spend the money because, "hey, it's for a good cause." If you really want to donate to a charity, then give the money directly to the charity...there's no need to line the pockets of a for-profit corporation at the same time.