I don't think the grand-parent poster said anything about preference. It may very well be the case that retention of information is better from dead tree books even though people prefer digital media. (Example: I'm sure most people would prefer to eat chocolate most of the time, but that doesn't really work out so well...)
That said, I think the accessibility argument is an strong one, especially if text can be read out loud and/or re-flowed properly (like on web pages) based on font size, but I honestly don't see why textbooks couldn't be provided both as digital and text. Surely the cost of producing the textbook is pretty marginal if you're already doing whiz-bang animations, etc. for the digital version? The bulk of the text should be identical, I should think.
That said, I think the accessibility argument is an strong one, especially if text can be read out loud and/or re-flowed properly (like on web pages) based on font size, but I honestly don't see why textbooks couldn't be provided both as digital and text. Surely the cost of producing the textbook is pretty marginal if you're already doing whiz-bang animations, etc. for the digital version? The bulk of the text should be identical, I should think.