His point is that title text is pretty much only available to most people as a mouseover tool tip -- not something most people see unless they are actually selecting the link. If I read between the lines of what he is saying, it seems to me as hypothesizing that most very rare exceptions, people don't tend to mouse over links they aren't expecting to click on in the hopes of seeing more information. At least, that would be my hypothesis.

While I can't assert the truth of that one way or the other, the fact remains that the title attribute is not an accessibility tool, except in those very rare cases (forms and frames). Physically disabled users who are using adaptive technology are less likely than able-bodied users to gain benefits from the title attribute, not more likely.

I suppose there might be benefits to cognitively disabled users from the extra information in the mouseover tool tip, although I've never seen that asserted anywhere. But if it were true, it would require training for those of us who write the pages and how to write good title text to accommodate those accessibility needs, since simply mirroring the alt text (which is what we currently do all over the site) is not going to add much functionality.