That's one of the most bizarre statements I've ever heard.
So, by your logic, those offering fixed rates don't keep a cut for themselves? Do AmazingMedia and ValueClick disclose the prices they receive from advertisers? Do you think their cut is any smaller than the minute 35% that FastClick accepts.
BTW, most advertising firms (both offline and on) are subject to intensive audits to verify the figures that they present their advertiser and publisher partners, in order to avoid the situation you are describing. In addition, many of these firms are publicly-traded, which makes their internal books (to some degree) visible to anyone who cares to go over the figures.
In the case of FastClick, in particular, it's clear that they are not deceiving their publisher base, since they sell their inventory at rates very close to their rate card - and we know that advertisers never pay the full rate-card price during a buyer's market.