Hi Adam,
According to Danny Goodman's Dynamic HTML book, <del> is supported by Netscape 6+ and IE 4+ and I can confirm that it works in Firefox 1.0.7 and Opera 8.02 so is it really that weak (I have not tested non-windows browsers which you probably have)?
Your example, however, is not really fair because you are not actually using <del> tags in your 'Use DEL' example.
Andy