When I've looked I've come across a complete lack of material for most topics beyond say third semester calculus and second semester differential equations that one can read to actually learn a subject. While there are certainly some example problems out there, a cohesive narration of how to go about solving more advanced problems especially with a consistent notation seems to be lacking. Sure there's resources like Pauls Online Math Notes, but that drops off before then. Wikipedia has some formulas and descriptions, but often doesn't have example problems. For many topics, you can find small pieces of information all over the web, but if you want to actually read up on a specific subject I haven't seen anything on the internet that rivals a good old fashioned text book.
Now, I don't see any reason for there to be new editions as often as there are. Many of the textbooks I read in my spare time are actually pretty old, but outside of some of the topics that rely on technology there isn't a whole lot of reason to have new editions. Even something such as numerical analysis (which should probably have a technology based theme for CAS) doesn't really need to be updated very often as the algorithms don't change, just the languages that may be used.
Perhaps I'm just biased, but a well written text book seems much more useful than gleaning bits of information from a variety of sources that all use different notations and symbols for learning about a topic in math.