I don't see how that's any different from what PC game companies do. You buy the game, then you buy expansion packs for it.
But I'm really concerned that it may not be the best model for e-books. For one thing, e-book prices are pretty tight already. What happens if Apple also gets to take a 30% cut?
For another, what about those apps, like eReader or Stanza, that allow you to purchase content from "within the app" already? How will they get by in a world where Apple has such strict rules about "in-app stores"?
http://www.teleread.org/2009/03/17/w...t-e-book-apps/