This is a little sleazy: if you bring your iPhone 4 in to Apple to get it fixed, it's likely to come back with new screws on the bottom. Screws that are impossible to get through unless you've got Apple's weirdo screwdriver.
This is to make it impossible to open the iPhone and tinker around inside it. Granted, most people have no real reason to ever do this, but a key part of ownership of something is having the ability to do what you want to it. By changing something you own in such a way after you've bought it, Apple is removing your ability to fully use your product.
Luckily, you can buy the fancy screwdriver online for a mere $10, if you really want to get in there.