Individual topics may not be more comprehensive, but the advantage of a book is that it puts all the pieces together systematically. I see a lot of people who’ve learned web design piecemeal on the web, and who thus have bigs gaps in their knowledge, because their learning on the web was about grabbing random bits of info here and there.
I’m sure everything could be found on the web, but usually the learner doesn’t know what to search for to make sure all the gaps are filled in. That’s why I recommend starting with a book, then moving on from there.