No there is no affiliate program for the Android Market.
Some individual apps that need to be side-loaded or have a seperate sign up for paid service offer affiliate programs but nothing through the official market. Lots of people ask about it at the Google support threads but Google has not announced any plans to start an affiliate program nor have they commented on why they don't have one.
I don't believe anyone is earning money for referrals if they are sending people to the Official Market, Appbrain, Cryket, AndroLib or SlideMe. If they are a commercial review site they are probably making money with display advertising, which incidentally improves the credibility of their reviews (because their income isn't dependent on you buying what they reviewed).