This is kind of like saying "If I didn't get into Harvard, why should you still go to college?" No matter how big YC gets, they will still be rejecting the vast majority of applicants. Its simply not possible for them to fund every startup that comes their way.

Furthermore, think of companies like instagram, angry birds, quora, github, groupon, and a huge list of others that are not YC companies, but kicking ass. Should these people have given up because they weren't in YC? YC is one of the greatest opportunities in Silicon Valley, but by no means is it the only game in town.