I have to play the role of defending Apple here if for no reason other than to try and point out where they 'might' be coming from.
I know it's in Apple's interest to have an iDevice in as many hands as possible. They want to lure as many people to their hardware as they can because there are many avenues for them to get additional sales. I think the issue they have is that Amazon is basically paying nothing to them currently for Apple's huge market for which they can get book sales, etc. I could be wrong but beyond making the app, what cost does Amazon currently endure with regards to selling all these virtual items through Apple? None, right?
Simply put, Amazon has a HUGE market they can tap into and get sales without really putting out any large expense. I'm not saying I agree with the 30% added cost (should be lower) but I see where Apple is coming from.
Now flame away.