A real world example: Simon Green's Hawk & Fisher books are available for Kindle in a $9.99 3-in-1 omnibus edition, price is $3.33 per book. An individual Nightside book sells for as little as $5.20, as much as $6.40. The Hawk & Fisher books sell fewer Kindle copies by far than the Nightside books. Which on the one hand, makes sense because the Nightside books are newer and ongoing while the Hawk & Fisher books are backlist items, published a while ago and not ongoing. But on the other hand, the books themselves are very similar, and my instinct is that there's a bigger gap in sales than there should be considering the unit price per book.
Is it possible that there are price-sensitive people who are so focused on price that they refuse to buy the Hawk & Fisher omnibus at $9.99, because that's 80% or 50% more than a Nightside book, without realizing that they're actually getting a Hawk & Fisher novel for half the price?
What would happen if Penguin stopped offering the omnibus edition of the Hawk & Fisher books at all, and just sold them where they'd sell for the same $6.40 as Hex and the City?
What would happen if they followed the Baen Webscription model, where you can buy seven John Hemry books for $5 each or seven in a $30 bundle? In my experience, Baen manages to drive a lot of purchasers toward the high-priced bundle because the discount suddenly becomes visible. Hardly anyone buys one book for $5 when they can save $5 by spending an extra $25.
My gut feeling tells me that the current pricing for the Hawk & Fisher books is the worst of all possible words, losing revenue to the price sensitive customer and to the less price sensitive cover by offering a discount that isn't clearly visible. I think if you had only single books you'd have some people who'd be upset they couldn't buy the same omnibus for an e-book that they could for the physical, but still end up making more money. The Webscription program suggests the best thing to do is offer both the single and the bundle even if you don't sell any singles. I know it would be a good idea for the publishers to start getting very creative and scientific in looking at these things when they have the control and ability to do so.