I can't seem to find the book to verify the phrasing in JSDG, but at the time I read it, it sounded like a lovely way of doing away with the repetitive typing of type attributes for all tags of those kinds, throughout the entire document. Great!
Well, not so.
The HTML DTDs still require those type attributes (if you want your documents to verify as correct HTML), and the purpose of those meta tags is purely senseless standards masturbation mode and not this convenient Don't-Repeat-Yourself way of specifying a type and character set in one place only (so my ;charset=UTF-8 appendix is particularly misleading). The intent? Well, they mark the content type of the tag attributes (onclick="...", ..., style="...") where the HTML standard already declares sensible defaults. The relevant parts of the HTML standard linked above are very fuzzily phrased in terms of setting the default language for a document, so the misinterpretation is certainly very easy to do.
Thus it's not the ideal marriage with the pragmatic minimalist Douglas Crockford's advice of just dropping those type attributes all together and have browsers and web servers do the right thing for you. If you want your web pages to keep working after you have saved them (and their relatively linked required resources) to disk, you'd better keep those type attributes with charset specifications, or your browser will have to guess.
Which might not have been such a bad thing, had they only guessed UTF-8 for anything that could possibly be UTF-8. Oh, well.