What does YCombinator give you?
-- Access to advice from more experienced people (in many respects: programming, architecture, business model, user acquisition, usability, user experience. It's rare for any startup to have 2-3 founders that together are rock solid in all these areas)
-- A name-brand incubator that helps you attract talent
-- A name-brand incubator that helps you attract high-value first adopters
-- Networking with other very talented YCombinator applicants and alumni
-- Plenty of news coverage from tech pundits and other journalists because of the YCombinator brand
I would bet you that the overwhelming majority of YCombinator applicants do not apply for the money. They most likely apply for all the other intangible benefits.