I believed the $15 price was like the $0.99 per track price they set. Interestingly, this means that if the publisher publishes elsewhere the most they can charge is $15 on iBooks. But if they only publish on iBooks they can charge more.... however school districts will likely have $15 competing textbooks to choose from. I don't think any textbooks are really proprietary, so it seems hard for $15 not to become the price they gravitate to... but I thought it was a hard price Apple was requiring and apparently it isn't.
Your quora answer is talking about when textbook versions are replaced. EG: Every 7-10 years they go from American History, 3rd Edition to American History 4th Edition (or 6th or a competing textbook.)
I'm talking about how long the physical books themselves last. EG: The school may stay standardized on the same edition of the book for 10 years, but replace their entire inventory completely 3 times in that period.
Your quora answer is talking about when textbook versions are replaced. EG: Every 7-10 years they go from American History, 3rd Edition to American History 4th Edition (or 6th or a competing textbook.)
I'm talking about how long the physical books themselves last. EG: The school may stay standardized on the same edition of the book for 10 years, but replace their entire inventory completely 3 times in that period.