Let's not think about patent/trademark issue for a second.

It's ludicrous why Amazon would name its store to something already similar. Whether or not Apple 'owns' the name, App Store, why would a huge company, with a clear brand, names its store that will only lead to customer confusion.

Are they trying to prove a point? Google's Google Play gives it a clear distinction, it even adds it's own name to the name. Why doesn't Amazon do this?

Short of trying to prove a point and sticking it to Apple, I don't see any merit for Amazon (not to mention it came after Apple's App Store) in naming its store Appstore. (or maybe they lack creative marketers to come up with a clever name?)