I'm not sure if this measure means much... with no downvotes, if quality goes down, "classic users" will simply vote less often. That would be a decently interesting statistic: (page views)/(story votes) over the lifetime of older accounts. Not sure if that data is still available, though.
Although it might be fun to create HN/postmodern where only votes from accounts less than a year old are counted, and compare that to classic?
Does this mean the problem at core could be with submissions and the moment it floats up to page 1 - which it would with just > 4 points in 3-4 hrs it gets reassuring votes even from old-timers.
PG, You should dig out the data on how lazy old-timers are getting in digging out material for HN front page :)