In a vacuum, they might be the same, although like someone else mentioned, with parens, you eventually get the dreaded ))))))) somewhere.
It's not in a vacuum though: there are tons of tools and tutorials and colleagues and other things dealing with HTML as it is, and tons of people used to how it currently is.
The original question, "how would sexprs make a better markup language", was in a vacuum. At least that's how I took it, and for good reason. A discussion whose pivotal argument is "well, that's how we do things now" is neither interesting nor (after the first few times your idealism is stomped on) is it illuminating.
