>
> Apart from your outstanding display of humour, I seem to have missed the 
> part where you explain *why* you think sub and sup are not purely 
> presentational...
What is a superscript letter/number is part of a name?

Take for example, the anime and manga Ranma<sup>1/2</sup>

Now I suppose you could write it as Ranma1/2, but that would be incorrect.

Same can be said for subscript.

So let's say that a web author has a list of  book if manga, either it's 
a reference site for these books, or it's a retail site selling them, 
doesn't really matter for this example.  The author wants to note the 
manga listed above, since he isn't using <sup> for presentation but 
rather as part of a valid name to a product, it becomes structural.