A lot of (college textbook) publishers already have ebook version together with the printed version, which usually costs about 75% of the printed version.
They are not that popular because most eBook readers does not offer annotation, and students don't usually buy the eBook even if it is available for that reason. Students like to be able to write notes on the textbook.
Maybe with the iPad's popularity, students will be more inclined to use eBook instead of printed textbook if they have the choice.
Another reason is that textbook publishers are into making money. An average college textbook costs $100, but they have to sell it at a lower price for eBook (even though they don't have overhead printing cost, yet they are not making enough money for it.)
One of the things I don't understand about this is that most students will buy used copies of books when they are available...some students will even go as far as buying a previous edition to save money. So let's say one book goes through the hands of 4 students through a campus bookstore buying and selling used books...Sure the campus bookstore makes money selling 1 book out 4 times...but the publisher is still only selling 1 book.
It isn't like you can buy and sell used eBooks so if they were all electronic editions...the publisher would have sold 4 books.
So I just don't understand why the publishers are so anti-ebook. I can understand why bookstores would be though.