[Not that I don't love excellent reference books! I love all kinds of books] If I ever write a non-fiction book, it will be a learning book!
Tim O'Reilly has been giving a talk on What Book Sales Tell Us About the State of the Tech Industry, and O'Reilly's extensive data crunching (for all publishers, not just O'Reilly Media) has consistently found that when a technology is fairly new, the bestselling books on the topic tend to be more advanced, less step-by-step learning. But as the technology evolves, the balance shifts and the bestsellers are the beginning books while the advanced books start to drop off. This isn't completely intuitive unless you think about who the early adopters are. So for example, the bestselling Java book today is a beginner book, and the best selling C++ books are also focused more on beginners, where a few years ago, the bestselling Java books were advanced reference books, not "learning experiences."