Let's go with Ivy League gives you connections. My alma mater has pitch events that are only open to alumni and the judges are active investors who are alumni. There is feedback, mentoring, networking, and money flowing in a system that doesn't even pretend to be open to the public.
"10-30%"
Seems awfully high. Still, that leaves 90-70% legitimate entries.
I think that if someone is a legacy at an Ivy league school (in the sense that you are implying) then that person probably isn't trying to lead the lifestyle that comes along with launching a startup.