It's an interesting result - it only counts upvotes by users from before December 2008 who are still active on the site
After all, if you changed HN into a My Little Pony discussion site you'd lose 98% of old users, retaining the 2% who like ponies - and thereafter, 100% of remaining old users would like ponies.
>>michae+(OP)
That's a good point. But there are a lot of users from 2008 still active on the site. It would be interesting to see how the attrition rate has changed over time, but I've never looked into that.