iTunes put it in people's heads that a song is worth $1. Amazon is working hard at saying that a book is worth $10. This is the same model - by setting the price for individual apps, Amazon is going to be setting the price for the entire industry. I'd assume Amazon would almost always price an app lower than developers would (and I doubt you'll be able to game the system by suggestion for 2x what you would have otherwise), meaning an overall downward pressure in app prices.
Would benefit users...seems impossible to tell whether it'll benefit developers (or whether other aspects of the store will compensate them, such as with increased sales).