The current phrasing doesn't restrict this to span. It allows "WYSIWYG
editors" to produce <p><font size=7>blah</font</p> where <h1>blah</h1> is
appropriate.
If I understand correctly, even that wouldn't be correct, because the only attribute specifically allowed on <font> is the "style" attribute. I don't personally know of any WYSIWYG editors that use <font style>. I know of some that use <font color> and <font size> as well as <span style> and even <big> and <small>, but none that use <font style> by default. As it is, it looks like the spec is trying to be backward compatible with something, but I don't know what. If <font> is allowed, then <font size> could be allowed, because a server-side script could more easily find <font size=7> and replace it with <h1>. Since I'm not aware which editors are being graced by allowing <font> without "size" or "color". Hopefully before editors start putting an HTML5 DOCTYPE on HTML files, they'll stop using <font> in favor of something else. Until then, they can happily put HTML 4.01 Transition (not even Strict!) on their documents that include <font>
