Actually, that's no longer true. The internet has made it possible for Obama to raise a lot of money without having to use a lot of money in the process. Obama's organization is incredibly effective at harnessing the power of the internet, and that's how he has gotten most of his money. With that money he built a large and very effective ground organization that has multiplied the effect of the money he gets online, which allows him to buy advertising, and that generates more financial contributions. But it started with the internet.