I recall from my venture class in B-school that most venture funds basically match inflation. Sorry, I don't have a link to cite, but our prof had been a venture capitalist for 15 years. For every $100M return KPCB sees off of a Facebook or similar, they pump $90M into companies that either fail outright or exit in a break-even acquihire. $10M over the average 10 year life of a venture fund isn't a great return.

Most good VCs aren't in it for the money; they want to see people succeed. The money is obviously important, but they generally have enough of it before they start investing.