Drupal does have great online documentation.

You clearly haven't tried to use it for anything... It's mostly out of date and referencing old versions (5.x and 4.x). Drupal is a great codebase, but they change APIs far too often to allow the documentation to keep up.

If you ask for advice in the IRC chat or on the forums/groups, you'll just hear "buy and read the book and don't write anything else until you've read it".

So yeah, "The Book" is an invaluable resource, I'm sure, but I'm with an earlier poster that said this sort of information should be available in their documentation. Physical books on programming topics should be reserved for the teaching and techniques, not the only place to get a tutorial on the basics.