yeah, we are bashing the same sandbag here. But that is a logical approach for google, if they really want to get rid of the dupes.
I wonder, if they applied that filter and said:
"well, some OK sites will vanish, too, but what will be left is really high quality"
That puts thousands of good sites into "danger" (are you working with RSS, too?), but gives Google an overall better index:
"You can't make an omelette without breaking eggs..."
Could be the name for this "non-update"-algo tweak.