It's a teensy-weensy, OCD/hobbyist fraction, of a sliver of the ebook-buying/reading public that will give two squats about the guts of your epub. The rest don't even know the book has guts to give squats about. So as long as it renders well on most devices (and the code doesn't look like pure soup), let your own conscience guide you about how nitpicky you ought to be about your code. The seven people your code could possibly offend will secretly be happier than a hog in mud that they have some new code to clean up and complain about anyway.
