I'd like those features too, but unfortunately for reference material I find annotation and pagination more important. Annotation is broken in HTML/EPUB because there's no way to make my annotations portable across devices without vendor lock-in. Pagination is broken because HTML documents rarely contain paragraph numbers or other useful pinpoints, and browsers aren't as good as PDF readers at keeping track of your position in a long document. These are solvable problems, but until they are solved I find HTML unusable for anything that takes more than 15 minutes to read. I suspect that most people who consider PDF obsolete rarely spend that much time on a single document.