This is the way they make money:

As of Q1 2008, YouTube was not profitable, with its revenues in 2007 being noted as "not material" by Google in a regulatory filing.[4] Exact revenue or profit numbers are not published, but a June 2008 Forbes magazine article projected the 2008 revenue at $200 million, noting progress in ad sales.[11] At that time, the price for an ad on the YouTube home page was $175,000 per day (plus a $50,000 commitment to buy Google/YouTube ads elsewhere), and a branded channel (distinguished by a customized background) cost advertisers $200,000.

http://en.wikipedia.org/wiki/YouTube