The presence of "freedom of choice" for the consumer depends on how you look at the industry. From a student's perspective, there is no real choice - you use the textbook you're assigned. Some professors will offer a few alternatives, but unless they're very diligent about always giving references to each book (and I had a few professors who did this well), the students who use the number-one book - the one the professor uses when he's lecturing and doing examples - will generally have a better idea of the material and the standard they'll be evaluated on.

From the professor's point of view (considering them as the consumer), however, there's quite a free market. They can get free evaluation copies of any textbook they want, and most schools give individual professors the choice of what book they use for a given class. So the problem then becomes getting professors to switch textbooks, which is tough. Most professors - especially in things like science - will teach the same courses year-on, and will become very comfortable with the material in a given book. They'll know what to skip, what to supplement, and what to offer additional comments on.