Jane_Doe is right.
But i can add that google does not guarantee any CPC percentage, and revenue can vary a lot depending on the site and size. Many expect that google is giving far more at launch to get critical mass before lowering payments as a percentage of clicks delivered. Also as more publishers sign on there is more competition for publishers maybe reflected in lower CTR and other aspects as time goes on.
Adsense is a great program for certain publishers, but it hasnt been going long enough yet for anyone to make reliable predictions of revenue medium to long term.
Is this "exclusivity" a new policy for Espotting? is it for your site as a whole, all sites you own, or by the page? I can imagine that many ad servers and affiliate managers will have to come up with some new ways to compete against the new google ad network if google can keep their commissions substantially higher than them.
Im expecting quite a big shakeout in the ad networks/affiliate area, same as google caused in the SE area several years back. This time though i dont think competing networks can afford to let their customer base run down, so they must come up with some innovative or more lucrative offers for publishers pretty soon. If I was them i wouldnt be waiting for Adsense to start reducing revenues to publishers, as every adsense ad contains an ad for advertisers to use Adwords, and this will drive up ad costs to advertisers as well, allowing publishers to maintain revenue.