Troymc's comment above catches my view pretty well. Some texts (I'm talking about fiction here, not magazines or other stuff) require quite specific formatting; most do not. Further, reader's preferences vary widely.
I would strongly prefer an approach that allows readers (the devices) to produce reasonable default layout while simultaneously allowing readers (the people doing the reading!) to adjust the defaults on their device to match their individual needs and taste. Finally, I want publishers to be able to specify quite detailed and complicated layout when necessary -- but only when necessary, as this should be quite an unusual occurrence.
Broad industry agreement on standard markup for the simple cases would be a great step in this direction.