I agree with everything you said but worry about the market dynamics of capping the price at $15. As far as I've seen, Apple has never done this before (putting a price floor of $0.99 for paid apps is quite different).
Will this result in each "chapter" being $15 eventually? Will this favor the rich student over the poor one in terms of coverage (underfunded school wants basic book that covers entire course, but marketplace offers much better books that are more surgical in coverage - rich kid gets better content while poor kid does not).
Hmm but since private schools already exist, a more granular way for families to improve their child's education by choosing to spend more money on it is surely only going to be an improvement. (no idea why you were down voted)
Technically, they did cap prices after the "I am rich" app.
Back to the subject: I expect prices will rise to whatever the market accepts.
On the one hand, that may be less than what it currently accepts, because a) people expect lower prices for non-physical goods and b) there may be more competition.
On the other hand, production prices for 'books' might increase by orders of magnitude if publishers insert lots of interactive stuff (but I guess many textbooks already ship with CDs or URLs, so that effect may not be that large)
Apple never actually capped textbooks at $14.99 (from my understanding). What they've done is launch with all the textbooks at $14.99 or less. They're setting a precedent and I'm sure they're hoping it pressures all textbooks to follow suit, but nowhere did I read anything about Apple requiring all future textbook offerings to follow the launch pricing.
Will this result in each "chapter" being $15 eventually? Will this favor the rich student over the poor one in terms of coverage (underfunded school wants basic book that covers entire course, but marketplace offers much better books that are more surgical in coverage - rich kid gets better content while poor kid does not).