I don't find this with mathematics at all. If I want to learn some new area, I'll begin by looking on the Internet, but the main question motivating that search will be, "what books do I need to read?" Most of the knowledge simply isn't (yet) online in the form it needs to be for real learning.

Google and Wikipedia are entrance doors. Just reading a few Wiki pages or the top Google hits is like never entering further than the foyer of a library.