I'm ambivalent about this idea. I don't think it's a good option for more technical textbooks at university level. Otherwise, it seems like a limited stopgap until the promise of the web is fulfilled. A concerted effort to make better use of the technology that is already available would be more beneficial to the majority of schools and students who can't spend precious money on iPads.
In any case, I still prefer paper textbooks. Apart from the cost, which which Apple won't address by pushing iPads and can be mitigated by not insisting that books are updated so often, I don't see a problem with them.
Also, they are really pushing the idea that textbooks are quickly out of date. This is simply wrong, especially at the level they are pitching this, and is just perpetuating the interests of the publishers.