The YC partners do not like the idea of being responsible for you leaving college. They are ok with it in the situation where you are so incredibly dedicated that you are leaving college with or without them. Or if you have some plan to finish while working full time on the company -- some of the Weeblies finished their degrees at PSU with online courses.
+1 Thanks for the insight. I've decided that I'm going to build this with or without YC. I'll able to take a leave of absence if I need to at school.