I'm not suggesting that Linux documentation is complete. (Although for all I know, it really is and I've just failed--repeatedly--to find certain information.) Writing good documentation can be almost as hard as writing good software, and as you suggest, the skills of a good programmer do not in themselves constitute the skills of a good technical writer. In reality, it's not particularly common to find those disparate skills in a single person. Add to that the multilingual nature of the user base and you've got quite a large documentation challenge.
Dangit, no "complete_intro_to_advanced_linux_usage_for_beginners_and_sysadmins_in_300_l anguages.pdf" file? :) The worst thing is knowing WHAT you want to do, and end up shuffling through 5 to 10 MAN pages, only to have someone tell you "Oh, so-and-so wrote an app to do that, apt-get XYZ and that's it"...