As another comment on here pointed out, just about everybody is missing the point of what Amazon is doing. This isn't something to benefit the customer - this is a monopoly move designed to wipe out any competition to Amazon in the app marketplace.
I'm going to discuss this in layman's terms. Now, for details on the contract, see this post, which shows you where things are on the contact and how they're working: http://developers.slashdot.org/comments.pl?sid=1951734&cid=34889086
This is an evil monopoly move by Amazon, and it isn't the first one. This is the third I've seen. The first was a move to wipe out print-on-demand printers used by the small press market - Amazon contacted several of the larger small press publishers and informed them that if they didn't switch to Amazon's in-house printer (a company called Booksurge known for shoddy printing jobs), Amazon would remove the buy button on their books. Amazon did pull that trigger, by the way, and it resulted in a class action lawsuit that put an end to that particular trick. The second was an attempt to wipe out any competition selling e-books - Amazon spun the dispute as greedy publishers wanting to price-gouge customers, but what it was actually about was that Amazon had tried to get publishers to sign contracts stating that Amazon would always get the lowest list price for e-books, regardless of any other arrangements past or future...including direct sales from the publisher's own website. The publishers fought that one and won, even though they took a PR hit for it.
This one is an effort to wipe out any competition in the app market by manipulating app developers. Here's how it works:
As the article said, the terms are set where the app developer will receive 70% of the actual sale or 20% of the list price (basically, the price the store is supposed to sell it for), whichever is greater. As was left out (and pointed out in the post I linked to), there's a clause in the contract stating that Amazon must always get the lowest list price.
So, if you're a developer, you need to calculate the list price of your product based on what you need to receive from each app sold. Let's say that's $4. But, with the terms of this agreement, you are only guaranteed that if it is 20% of your list price, so you have to set your list price at $20. Therefore, if Amazon turns around and sells it for $4.50, you are guaranteed to get your $4.
But, this also means that in order to ensure that you get that $4, you are now forced to overprice your product. So, everybody else who carries your product - including yourself, if you have your own little app store - has to do it at a list price of $20. In the meantime, Amazon can set the price to whatever it wants, and so long as it doesn't go below $4, it will make a profit on the sale. And, Amazon even makes it look like it is doing you a favour - after all, if your app sells for $10, you're going to get $7 from it. Amazon gets to have the lowest prices, and you - the developer - have made it so that every other app store gets thrown under the proverbial bus when it comes to your app, because they will never be able to compete while using the list price that you are forced to give them.
This is an incredibly dirty trick, and what needs to happen is that app developers need to fight back and refuse those contract terms en masse. If they can do that - like the publishers did with e-books - then Amazon will be forced to back down. If they don't, then Amazon will stand a reasonable chance of not only gaining a monopoly position, but actually wiping out any competition.