YC is working on addressing the problem of funding Watsi's overhead. The point of the service is that end-users don't fund Watsi, they fund patients. In the same sense as you need to take it sort of on faith that Airbnb can bootstrap and maintain a two-sided market for short-term lodging, you should probably take it on faith that Watsi's model is going to work; if you want to make Watsi work well, go fund a patient with it.
There is a real 13 year old girl on Watsi right now who is unable to walk because of a correctible congenital condition. Who cares about the Watsi founders? Go help the girl! :)