To quote from the phpdoc:

	 * @param string $value Thingy goes into a wikitext table; it used to be escaped but
	 *   that was incompatible with previous practise of customized display
	 *   with wikitext formatting via messages such as 'exif-model-value'.
	 *   So the escaping is taken back out, but generally this seems a confusing
	 *   interface.

It appears that in general $value is expected to be wikitext, but in htmlspecialchars is usually used to escape raw data from EXIF tags, etc, instead of wfEscapeWikiText so that URL auto-linking occurs, and parameters to messages are not necessarily consistently escaped.

I think addMeta() should specify that the values are always wikitext, and we should have a helper method somewhere to do the 'almost-escaping' correctly.