The only reason I keep gently nagging away about this is that I am lazy and would like not to have to do this myself every time I want to read a PG book on one of my e-readers
Better reasons to keep nagging include a) only 1 in 100 (to be generous) PG customers know how to do this and b) PG books get repurposed by many publishers including Apple, B&N, feedbooks, and Amazon, but while largely "thowing away" PG volunteers' formatting efforts because it is not done in a reliably consistent and usable way. When these republishers substitute their own automatic computerized formatting, the result is often even worse.
I should make it clear that my advocacy of somewhat standardising the current large PG catalogue of HTML is not intended to imply anything general about the excellence or otherwise of HTML as a master document format.
Again, a practical problem is that most texts come from DP, and there is a large contingent of self-proclaimed "HTML Masters" at DP who are actively hostile to being required to make any restrictions on their idiosyncratic usages of HTML in order to make PG books actually readable on e-book readers.