I'm guessing you're correct, though there is a method of correllating physical page numbers with documents in epub. I'm hoping this isn't a fixed length only thing or an iBooks Author only thing. For legal or educational books, having the ability to reference a specific page that's the same as it is in print is very important. As a matter of fact legal citations often reference page numbers.
So far Apple is doing a good job of providing a book reader that does more than novels, I hope the addition of page numbers is one of them. Note I have tried the epub method, but I can't get it to work, so I'm not sure if I'm messing up with the coding or if this isn't supported.