I thought about that, Donna - especially since Google does generate website taxonomies. It did seem they might have targeted certain taxonomies and not others.
However, there probably isn't a lot of practical difference - big traffic sites were going to get checked out either way. And since "content farms" were at least part of Google's motivation, they would go after all kinds of information, and not just ecommerce.
In fact, the early Panda comments from Google were often about how trusted a site's information might be - lots of medical examples, for instance. So coupling that with the explicit mention of "long tail" I lean pretty much toward query volume as the selector for Panda evaluations. From what I see, even heavily Pandalyzed sites can still get rankings and traffic for extremely low volume or long-ish queries.