I've seen those dates showing up for the last 2 to 3 weeks. It seems to be site specific.
You can replicate it on some larger domains, like by doing a site: query on a certain cable news network.
I've been watching it because Google's abortive attempts at fixing some of their current conundrums have briefly resurrected several dropped pages of mine with those same dates such as:
www.domain.com/ - 27k - Aug 03, 2006
Even though those pages disappeared again after a day or so, it gave me some hope that when Google finally gets things fixed my site may benefit thereby.
Of course it could mean something entirely different or nothing at all.
I've mentioned it in this forum, but you're the first one I've seen who also noticed and commented on it.