I might have been wrong then, but I an certainly wrong now. It's a lot easier to make coffee table books for the iPad now. You can now use the Baker and Laker frameworks as the basis for your app, and Apple have enabled a full screen option for iBooks. Before this new option, iBooks forced you into a basic page layout which precluded complex formatting and full screen images. Now you can do a full screen image like you would see in a coffee table book.
If you'd like to see an example of a coffee table book on the iPad, check out Liz Castro's Barcelona: Beyond Gaudi. I can't find it in iTunes just yet, so you'll need to get it here.
My point here is that if there's a type of book that you believe can't be made into an ebook, wait 6 months then it will be doable. Wait another 6 months and it will be common.