<small>, like <b>, <i>, and now <s>, was traditionally presentational.  However, there are valid semantic reasons to make text small, just as there are valid semantic reasons to bold or italicize text.  In some cases we capture those semantics specifically, such as with <em> and <strong>, but it's not always worthwhile to mint elements for such specific, low-use semantics.  <small> captures the semantic of "fine print" and similar things, where the smallness of the text relative to the surrounding text is actually communicating useful information in visual media, and the semantic can be expressed in other media as well.

I think it's a bad idea to re-use elements that were primarily seen as presentational, and then re-define them for new semantic purposes. The web will then consist of uses of the same element for presentation, and for some form of semantics. 

The small element has traditionally been used to create smaller text, not to highlight specific fine print in a document. In HTML4, which probably accounts for a significant number of web pages today (and long into the future), it means nothing more than small text. It's use was discouraged in XHTML, because it was presentational. 

And now, small somehow has "meaning". Where before we discouraged its use, suddenly we're now telling web authors, designers, and developers that it's OK--but it's not the same thing. 

People have used the element, even correctly in HTML4. When people go to port their web pages over to HTML5, they'll ignore the small element use sprinkled liberally throughout their documents. And since it is a valid element, they won't get warnings, but their use will not reflect the new meaning within HTML5.

If we really feel the need for something like a fine print element (though why we would is extremely debatable), then it would have been better not to attempt to re-use existing elements, just because the previous element matches the expectations about presentation.

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Status: Rejected
Change Description: no spec change
Rationale: CSS has no way to indicate that text is legalese (aka "fine print"), and indeed should not have such a mechanism, since that is a semantic concern, not a presentational one.

The HTML spec does not define <small> as being for reducing the font size any more than it defines <h1> as being for increasing the font size.

http://www.w3.org/html/wg/tracker/issues/136