Pubmatic CPM report very misleading

This report by Pubmatic was passed around the office today.  It says that, according to data gathered from the 3,000 sites that Pubmatic manages ad inventory for, small sites earn a higher eCPM's than the larger ones.  Many people, including commenters on techcrunch, seem to think that this is because smaller sites have more targeted demographics and therefore get higher CPM's.  This is only partially true.  The main reason is depth and frequency of use.

The information Pubmatic is offering is only the ad network 'unsold' inventory and not ads the sites sold themselves or through other channels.  One thing about ad networks that you may not know is that they highly value the 'early' part of a site experience and pay far less for the 'later' impressions.

Translated: Consider 2 sites that are exactly equal except one has an average pv per unique of 5 pv's and the other 10 pv's.  Site one with only 5 pv avg will earn a much higher eCPM than the site with 10.  Ad networks earn (and therefore pay) less on the later impressions. 

I am making an assumption here, but I think that the larger sites Pubmatic manages have a deeper and more frequent readership than the smaller ones do...especially if any of the larger sites are social networks.  That is why these numbers are so off.