That's not correct. The top funds have very high IRRs. For example, Foundry Group on slide 5: www.scribd.com/fullscreen/57221228 . I remember Marc Andreessen describing A16Z's first fund as returning >100% IRR. I'm sure SV Angel's is very high as well.
In some cases, one or two investments account for most of the returns.
That's not at odds with a fund being successful. Startup investing is inherently about finding outliers: http://www.paulgraham.com/swan.html . Its alright if the median investment returns nothing as long as an outlier can return the entire fund. You might disagree with an entrepreneur aligning herself with investors that have this sort of thesis, but it's not accurate to say that the top funds perform poorly as a result.