Well I'm tutoring again this semester and have picked up a bunch of math classes.
One thing I've noticed on both the math and the programming courses is that the lower classes' books are just down right crap. The examples and problems they give are as clear as mud, the book itself is cheaply made, and there is nothing interesting in them.
My calc book has a bunch of side information about different things such as applications of ideas, tid bits on the history of the people that developed some of the theories, etc.
You'd think that the lower books would be better made since they are more important, but nope they find the biggest moron they can to write them.