I think when I said "People think about these mediums visually" I was saying it the wrong way. People think of these in terms of example, and symmetrically with reading. I know what things are appropriate as italics because of an intuition I've developed with reading. Ditto punctuation and smiley faces. I don't understand the rules behind these. I could understand them, I could probably make something up if you asked, but I don't write based on rational rules. I think this is generally true of writers. I might even venture a guess that people who aren't comfortable writing often don't have that intuition, and attempting to simulate intuition with rules is difficult and distracting.
My intuition says slanty-letters. If I read HTML source all the time, I might develop an intuition that mapped well to the em tag. Admittedly I don't see i either, but at least the mnemonic is better. And ReST is better yet, because I do read *italic* stuff often. (But is that italic or bold? It can be both, really)
I also hate instant messangers that put in smiley faces. They are horrible. The smiley has become a valid (and very important) form of punctuation. Punctuation should have symmetry. I should see it on my keyboard, see it when I'm typing it, read it when it's sent to me. But then I seriously doubt anyone here would actually support the graphical smiley faces, so this is an empty rant ;)