sgt, I am seeing this on 11 year old sites too. I am not sure since when google is collecting or using those metrics but the effect is similar on sites irrespective of their ages.
I am also not sure on how they collect these data. Some claim that it is through google toolbar but like every other argument that one dept. in google might not have access to data mined by another dept,we can make a similar case for this one too. They could even be deriving these metrics from the content, but who knows.