Most businesses won't put Adsense on their page, since it doesn't look as professional. Not to mention, Adsense is contextual advertising, so when a business puts it on their site, they are advertising their competition.
Dreamhost seems to be doing okay with their hosting income anyway.
If you're talking about paid ads that come up in a Google search, those would be affiliates that are advertising their referral links or promo codes through Google Adwords.
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