The purpose of the support handbook is to teach people how to work with the forums, and how to participate in documentation on the codex.
See the table of contents on the left.
Perhaps you were looking for other documentation?
The User Handbook, which is about using WordPress to create a website, write a blog, etc is here: http://make.wordpress.org/support/user-manual/.
There is an effort underway to document the WordPress codebase . You can find this at http://make.wordpress.org/docs/handbook/.
Handbooks for themes and plugins are here: