"By requiring that kind of thought, we are weighing down the author whose effort should really be directed towards writing, not towards typography"
Exactly. I once had a univesity prof who wrote his own textbook. He was free to sprinkle italics and bold and underlines wherever he pleased as he wrote. Unfortunately he knew nothing of typography. The result was a text that was a mess and near impossible to read.
Now what if this professor made an effort to simply indicate which words were titles and which phrases required emphasis, etc. ("semantic markup")? Enter one skilled typographer to create a stylesheet prior to printing. The result is a beautiful volume that conveys precisely what the author intended, but free from his primitive, ad-hoc typography.
1 vote for semantic mark-up. I've done it both ways and semantic wins every time.