What YC does, we have to do in person. Kind of like a university. So founders have to at least be able to get here for the 3 months. They could return to their home country after that, but they'd be more likely to succeed if they stayed in the US-- partly because it's a better environment for startups, and partly because it would be easier for us to help them.
Thanks for the comment pg. I will apply for the next YC funding cycle,and will bother about the Visa and all after getting called :-).