The HTML that DP has produced for years and is still producing does not work well on the new portable reading devices.
HTML does have the problem of not being perfectly matched to what we want to do -- it has many featured that arguably shouldn't be used in coding books -- but are -- and it is missing other features necessary to do the job well, most notably (to me) its weaknesses in coding poetry. BUT, a more serious problem is that PG "coders" don't agree on what should or shouldn't be coded. You can't create a better standard until there is much better agreement about what should be coded -- and what shouldn't be. Finally, authors and publishers do things in books where it isn't at all clear (to me at least) why they did what they did -- and how do you code those things, other than literally? Not to mention the problem of figuring out how to code that which appears to be coming from an incompetent original typesetter.