Is everything else between these two groups completely equal? I seriously doubt it is, in which case I don't think it's fair to make any conclusions that hold weight.

This is one of the problems I have with these sorts of things. My company went Agile about two years ago, and lots of people like to rant about how much better everything is now and how much more productive we all are because of it. Except we actually have no way of knowing whether it made any difference at all.