Yes, Amazon publishing allows its authors enough profit, because Amazon has to account for all of the expenses that are involved with running their website. They have to process sales, customer service issues, and returns. I sold a book through Amazon and I thought my profit rate, even for an e-book, was very fair.
I'm taking Amazon's side on the issue of payments to publishers and authors because it's supply vs demand issue. Amazon is offering a price that meets their marketing and sales goals. It is up to the authors and publishers to either accept the offer or sell their books via other outlets. Amazon, or any other business, is not obligate to ensure their suppliers makes a profit.
Yes, I think Amazon gives writers a very fare rate. I think Amazon has been very fair with the way they have dealt with publishing. I think authors are very lucky to have such access to a wonderful website suck as Amazon.com. I think the publishing business has changed forever.
I do not believe Amazon allows it's authors enough profit. I recently looked up the payout for this work and the pay off can be minimal, but it's also a question of quality. The way Amazon allows basically anyone to publish means there is a flood of writers. This can lead some people to believe they're being under paid when really they have to business writing. However, the secondary problem is the fact that better books often have editors, some thing that isn't taken into account with the payment system.