With today's announcement that Apple will be entering the textbook industry, some people on Reddit were wondering how Apple can possibly charge only $15 for textbooks and still convince publishers to get on board, when they're in the business of selling textbooks for anywhere upwards of $80 to $150 dollars. We can figure it out with some simple math. Let's take a look at my own high school biology class. Obviously I'm not a teacher or a student anymore, but let's use it as an example.
I honestly don't remember the name of the textbook we used, but let's say for argument's sake that it cost $100. A typical class at my high school had around 32 students. It was held 4 times a day, two semesters each year. That's 256 students per year.
But it was also a huge textbook--about 3 inches thick--so it was unreasonable to expect students to carry their own copy. Instead, we only used them during class, which means that, even accounting for having extras for the teacher or in case some were lost or damaged, we probably only had like 50 copies. And they probably got replaced about every 5 years (even that's generous, it was probably more like 7-10 years). 50 copies at $100 every five years is $1000 per year spent on textbooks.
With the iBooks model, Apple mentioned that [paraphrasing:] "each student gets to keep their book" which is really only true if each student owns their own iPad. The new iBooks app also includes many features like highlighting and note-taking that are really only useful if each student has his or her own iPad. If you assume that, then you can calculate that for the same class, Apple would be selling a new copy for $15 to every one of those 256 students per year, which works out to $3840 per year.
The real question isn't how the publishers can afford to use this model, but rather how the schools can possibly afford to. Schools are the (ahem) textbook example of chronically underfunded organizations. If Apple is really serious about being a driving force in education, which their presentation implied very strongly, then they can't expect to charge almost four times as much to the schools.
The only way this is going to take off in most public schools is if the iPad textbooks are as cheap or at least not hugely more expensive than paper textbooks on a per-year basis. If iPad books really are more engaging and useful then extra cost can be justified but school budgets can only be stretched so far. If schools are "checking out" iPads to students, either on a daily basis (use it while you're in class) or even a semesterly, yearly, or four-yearly basis, then you have to factor in the cost of the actual iPad hardware which, much like paper textbooks, will occasionally have to be replaced or upgraded. The success of iBook textbooks is going to depend on Apple negotiating a bulk purchase plan for both hardware (iPads) and software (the textbooks) which is beneficial to both the schools and the publishers.
Can Apple do it? Absolutely. Can they do it and still maintain the profit margins they're used to? Maybe not. Only time will tell, I suppose.