Every publisher believes that the e-books don't really compete against one another in price because each one is unique. They aren't interchangeable...someone won't say "wow, I bet I can get this same book cheaper somewhere else..."
But they are wrong. Lately, people have been able to get the same book cheaper by buying a used physical copy (still cheaper even after shipping costs). But, apart from that, when the price of a book exceeds the potential customer's sense of the book's value, they absolutely will buy a completely different book instead.
No product is immune to market forces, which is a good thing, and price-fixing harms the majority.
I don't agree. There are certain authors whose books I buy as soon as they are published. In the past this meant buying a hardback edition which is more than twice the cost of a paperback.
Books and other works of creative art are NOT fungible. You can't just replace a novel by your favourite author with a cheaper alternative in the same genre..