If the success rate for VC funded startups is 18%, then I could easily believe the overall rate is 10% or lower, because angels fund more startups than VCs, and they are less selective.
More selective doesn't necessarily mean a higher success rate, if VCs can't pick the winners at a higher rate than their general frequency in the population. Wasn't there just an article on here about how VC-funded "A teams" do no better, and often worse, than VC-funded "B teams". And I thought your "Unified Theory of VC suckage" mentioned this too, though rereading it, it seems more about how VCs take winners startups and make them fail rather than how winners avoid the VCs to start with.
That said, my high school math teacher and first employer was an angel investor, and he said his success rate was *well* under 10%.
A lot also depends on your definition of failure. When Ludicorp shut down Game Neverending and launched Flickr, would that count as a failure? If they had taken millions in VC funding, would they have been able to shut down GNE and say "We're going to build a photo-IM client"? I'm currently working for a (profitable) startup with 4 products. Only one of them is generating any revenue. If that had been VC-funded, it likely would have been 4 separate companies, 3 of which were failures.
