I agree. The books still have the authority on the subject, but to get at the real crux of all the information contained requires an investment of time and thought that isn't really necessary today. There are updated books dealing with the zone system which appropriately tackle its creative application, in today's context of 'getting results'. But, it definitely is a choice to invest in them, when you could be learning a lot more about yourself, practically. It's dangerous to be competitive in photography, especially as a hobbyist, but while you're pouring over those books, just remember that somebody else is out making great pictures, simply with a good intuition about tonality. They've likely spent more time looking at and making photographs than reading manuals. If you're planning on becoming a teacher or leading printing workshops, reading and re-reading Adams' books is definitely advantageous.
I just hope that I never employ an electrician to rewire my house who learned his trade on the internet.