Sorry, but I don't understand this comment. If exit size is not one of the primary metrics VCs look at and how they define success, I'm at a loss for what would be.
More specifically, how do you think USV and Fred define success? Fred says that financial returns (hence exits) are important on his own btw [1]
[1] http://www.avc.com/a_vc/2010/06/how-we-measure-success.html