Joined: 13 Jun 06
22 Jan 07 4:41 am
I don't think it's a case of Google penalizing your site by paying you less for each ad. I think it's possible that they're looking at the quality score of your site and not giving you the high paying ads. Instead they might be giving you lower paying ads or newer experimental ads that haven't been seen to be successful yet.
When I say "quality score" it's not just talking about your pagerank. It's also about your site's age, whether it's well siloed or not, the relevance of your material, whether you're using latent semantics to bump up the relevance, the quality/relevance of your inbound and outbound links, whether there are any trust sites or .edu sites linking to you... etc.
As others have said, you'll also find cost per click for content match to be lower than for search match. It's less targeted, and advertisers can bid lower for these. It's also possible that the ads you're attracting with your content are naturally low-paying ads.
My advice would be to work on making yourself look good to Google and see if it picks up. Also check that your topic looks profitable.
Hope it picks up!