I don't see where Fred says that exit valuation is a metric. His blog post on the subject never includes the phrase "exit valuation".
http://www.avc.com/a_vc/2013/09/maximizing-runway-can-minimi...
http://www.avc.com/a_vc/2013/09/maximizing-runway-can-minimi...
Fred talks about he defines success here - http://www.avc.com/a_vc/2010/06/how-we-measure-success.html
"We are financial investors and we do want to see our portfolio companies become valuable."
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