lucy24 - 5:41 am on Sep 18, 2012 (gmt 0)

Size is not the only way to show emphasis. That's why I detoured to Lynx while checking html-without-css handling of headers. <h1> is definitely in a class to itself, but all the others are still distinguished from each other and from regular text, even though they are the same size, color, weight and so on.

You could set
{font-size: 100%; font-weight: normal; font-style: normal; font-variant: normal; color: inherit; background-color: inherit; text-align: left; display: run-in;}
et cetera and it would still be a header semantically.