I think publishers pre-load overhead costs onto any edition of a book, hardcopy or electronic. I'm not saying it's right, and clearly they're capable of using a scaled approach because hardcovers cost a lot more than paperbacks (and I don't believe every bit of the added expense on hardcovers is production cost). I think the problem is that publishers haven't truly committed to ebooks in general, so they haven't bothered to make them a more attractive product line. Ebooks still comprise a tiny piece of annual book sales, but I think it's inevitable that the situation will change.
I released both my novels in Kindle, .pdf, .prc and trade paperback editions. The Kindle and paperback editions are selling, but I've yet to sell a single copy in .pdf or .prc. I assume this is because the Kindle and trade paperback editions are listed on Amazon and therefore have higher visibility, while the .pdf and .prc editions are only available on my web site. Whatever the cause, this lack of sales has discouraged me from looking into tools to convert my books into additional ebook formats. The situation raises another issue: lack of standardization in ebook formats. In my own experience, getting my books into many different formats is kind of a hassle, and not worth the effort if those formats don't sell.
April L. Hamilton