Chapter 16 of White Space is Not Your Enemy and Chapter 9 of Writing for the Web are the "wrap up" chapters. They give a nice little summary of what you've learned, answer some additional questions, and point you on your way to additional learning.
Their main point?
You have only uncovered the tip of the iceberg.
You are never really done learning in your chosen field.
These books are great for what they are, but they are not advanced knowledge, and you can't learn all there is to know about writing or designing for the web in a single book. It takes lots of practice, and lots of other books, and lots of time. And then lots more time relearning things when monumental technology, software, etc. is released. The only thing worse than knowing nothing is knowing enough to think you know it all, and royally messing up your projects.
With the huge amount of resources out there on the web, there's really no excuse for not knowing. If you can't learn by reading, learn by watching YouTube videos or downloading trial editions of software. See what others are doing, and see if you can mimic it to learn. See what others are doing badly, figure out why it's bad, and don't do it. Sign up for a newsletter, ezine, or magazine. Finally, there are plenty of creative communities out there - Livejournal communities and DeviantArt, among the hundreds - to help you hone your skills, see others' work, and get tips.