That was my thought also.. I don't mind supporting authors when they are not wringing every dollar they can from you. That is my argument with a lot of academics - they want to be published but how many people ever get to read what they write? Probably a handful of libraries that are on grants buy these expensive books and its read by at most a few hundred people.
If they published with a regular publisher (assuming it was good enough to be picked up) or even if it was self published it could be released for a reasonable about and get a much wider circulation. There are tons of books like that just gathering dust with interesting approaches that could be useful but they are never going to be read by anyone that would actually put it to practical use its a great shame.
Springer are a good example, they have a computer science series that runs into the 7000 volume mark now but nobody I know outside of a university has heard of it, But then things have started to change recently because these publishers were forced to move into the 21 century and give subscribers a better deal.
anyway rant over.