Paul Graham also stated that Silicon Valley is impossible to be cloned in Europe. That doesn't mean successful start-ups can pop-out in Europe. And they have, Skype, AllPeers, Six Apart, NetVibes, Fon etc...
Successful single founders is necessary to encompass a lot more characteristics. It's difficult enough to find 2 motivated people to take risk starting up, finding 2-in-1 it will be a lot harder. But if they try to avoid it, althout they don't exclude it, it doesn't mean it can happen at YC, or someone on his/her own.
