We believe 35% should go to the author, 35% to the publisher and 30% to Amazon. What do publishers even do with regards to e-book distribution? Are they going the way of the record label company?
Second, publishers also make losses on books that don't sell and that they have to recover. The majority of books don't actually sell a whole lot of copies, so the fixed costs associated with producing a book can be a pretty high percentage of revenues for the average book.
Finally, publishers provide editing, translation into foreign languages or negotiation with foreign publishers (assuming your agent didn't retain translation/foreign publication rights), production, marketing, accounting and sales services, distribution, and warehousing (for dead tree books).
Note also that you can equally ask what Amazon provides with regards to ebook distribution: In the end, it's just another middleman that got a head start because it was first to market with the Kindle, but is otherwise unnecessary. In some markets, publishers selling directly to readers (on non-Kindle platforms) makes up a significant part of sales.