They're not asking for exclusivity; you can sell the same app elsewhere. I wonder how long until they start offering sweetheart deals in order to get an app that no other store has (like they have done with some ebook titles)?
The income split is rather interesting. Amazon ahttp://the-digital-reader.com/wp-admin/post-new.phpre promising either 70% of sale price or %20 of list (whichever is greater). It sounds like they plan to price the apps aggressively in order to compete with the official Marketplace.
Personally, I can't wait. This is going to be the one app store where I know I'll be able to find everyone's app. There are a lot of reading apps that you can't get outside of the official marketplace.