The trouble is that this technology has a looooong way to go before it can even get close to an ordinary teacher. If you've ever had a good teacher who cared about your learning I think you know what I mean. There's always a slight excitement to receiving personally-directed communications that will be noticeably missing from any automatic spoon-feeding loop.
I have heard this situation being referred to as the '2 sigma problem', that is, if you train someone to do a task one on one their performance will be on average 2 standard deviations (of a class of learniners) better than if you did it one on many. The goal of CBL is therefore to produce teaching communication software so sophisticated it passes the Turing test (people cannot distinguish it from a person) at which point your improvement in training goes up '2 sigma'. But that assumes students are motivated to do well on a piece of software.
I would go further than Martin here in the importance of the person in the system, IMHO it is a central human feature to wish to impress people, be that a tutor or another student. Advanced CBL will only work as a carrot if a tutor is following your progress or you can turn to a fellow student and compare scores. Or if your boss sees your grade and gives you a raise (which is training not higher or school education).
Of course it is entirely possible to teach yourself with no interaction with other people by just using a good text book. IMHO any teaching technique that doesnt involve people is JUST a glorified text book.
This is not a chriticism of RuAE, I just like the topic area and writing or talking about it is my learning style