Also from a marketing point of view, Apple will want people to see other people using iPads. When Apple cover up all the sides and the back with their old cover you just look like your carrying around any other tablet. Which doesn't keep reminding people without iPad's how much they also want an iPad.
You are forgetting that no matter what tablet you have, be it Motorola Xoom, Samsung Galaxy whatever....people will ask you "Hey, is that the iPad?"
I had someone ask me if my KINDLE was an iPad.