there is lots of sites trying to make money through google adsense, but some are playing some more brilliance, they are using adwords to getting traffic to there site, yes they may be (70%) of them are making money, because they are experiece adwords marketer, so they know how to beat the adwords price, they find keywords with small bids in adwords, then they add big keyworded adsense, its a gambling...dont play with it, if you are not a adword expert..
vinodkv