You miss my point. I was talking about writing, not reading. Of *course* bold and italics emphasise things when you are reading something in a visual medium. That the whole point of them.
Ian seemed to be saying that when he writes something, his motivation for putting something in italics is that he wants it in italics, not to emphasise something. That's something the Robot Wisdom guy keeps saying, and it's not something I agree with.
As I said before, I have a tone of voice in mind when I write - that doesn't mean that when I use EM elements my primary consideration is how the page will sound when read aloud.