The test has to be what your users understand that value to mean. I'm betting almost all Posterous users think they're being read by significantly more people than they actually are.
If Posterous can't provide meaningful stats (and I appreciate that filtering out bots may be non-trivial) then they should just avoid providing stats altogether. Bad data is worse than no data as it's much more misleading.
For a site whose key value proposition is vanity - is it really? HotOrNot scales all ratings by (rating / 2 + 5.0), i.e. everybody's above average. According to the post by James Hong where he mentioned this, they seem to have found a notable increase in user satisfaction with the change.
Is it any different from Victoria Secret bras running a cup size or three higher than everyone else, or dress sizes continually shifting downwards, or SAT scores being recentered upwards by 100 points?
I agree with you, but no company's going to leap forward and be honest about numbers, they're going to use whichever makes them look biggest/growing strongest to their users, investors and competitors, and all the numbers are "right" in some context.
"Our goal is to be 100% transparent with everything we do at Posterous, especially when it affects your blog and content"
-Sachin cofounder, posterous.com
If Posterous can't provide meaningful stats (and I appreciate that filtering out bots may be non-trivial) then they should just avoid providing stats altogether. Bad data is worse than no data as it's much more misleading.