I've always wondered this. I'm in the midst of wedding planning, and I've already registered at a few places, but I stopped to think about it the other day. Why do we register? We're basically making a list of things we want, just out in the open? We're asking for specific gifts, which can be perceived very rude. It's not mandatory to buy from them, but the overall concept is strange.
In most countries, you literally give money to the couple, and they use it however they wish.
I always thought it was interesting...