It's all to do with the number of impressions. Some are on click, but
few are these days (because of what you suggested).
The ad revenue sucks (all though it has got better since the new
server came on - I suppose the improved speed of the server has
increased the number of impressions on the site people make)
Don't go refreshing your page though, the site performance is more
important that any spare change we get from the ads. I quite like the
ad server we have though just because I can slot my own ads in there
too (as I'm sure you had noticed - the 'pawn star' banner has been
shown over 6000000 times itself - in the boom days of dot coms, I
could have been rich with that much ad inventory!!)
-Russ