However, you can't just go to your office and bang out a new textbook on your Mac. This is particularly true in freshman and sophomore level courses. Textbook development is an involved process involving co-authors, editors, advisory panels, and many, many more. For K-12, you have to pass muster at other levels. State textbook adoption agencies play a huge role.
This technology stands to dramatically improve the process. However, its truly huge impact will come in supplementary materials. K-12 and university instructors will find it much easier to produce and distribute custom materials for their classes.
I think your point is valid in the near term, but go out 10 years and I think you'll see a very different landscape. College, first of all, is very different from K-12. Professors often write their own material and have it used by colleagues and themselves. So I think the first changes will happen at this level in education. The K-12 will, granted, take longer, but it will happen for the very reasons you listed above, in particular, the State adaption one along with all the other 'pass muster' reasons. The adaption process has evolved to a point of pedagogically correct texts that is driven by only a few States. What California, Texas, New York and Illinois adapt become the default texts for many smaller States unable to command attention/control of the publishing giants. What I think will evolve, particularly regarding Charter schools, is the adaption of a different text/content vetting method than just what's handed down by adaption boards at big States: college professors writing material themselves for (to begin) select high school curricula. The politics and finance of textbook purchasing has gotten to the point that many districts/schools/teachers would welcome an option that made better business sense. Finally, I don't see the large packaging that we have now continuing. Teaching Geometry, for example, wouldn't mean necessarily a full huge text placed in digital form. Rather, I think you'll see a more eclectic ad hoc approach to the content as defined by a State standards body. Shopping around for how you address that, textwise, is where the change will come. This is going to happen regardless of what Apple comes up with next week.