People can write ripoff books that are different enough to be free from recourse. In HTML5, the platform is even more narrow than natural language. A "thief" has available to them all of the approaches, quirks and libraries of the original author -- none of which is exclusive.

Together with the lack of practical enforcement, there doesn't appear to be any utility in the law. Saying an HTML5 web app should be protected by copyright is a bad joke at this point.