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.
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.