YCombinator's application is not hoop-jumping. It's training. These are questions that you should be asking yourself about your idea anyway, regardless of whether you seek YC funding. Big-time VC funds will ask you the same questions, except that they require a personal introduction to even get to that point. Heck, customers will ask you the same thing, except that they want you to show them the answers through your product instead of tell them through an application form.
Also, the value of YCombinator is not in the $20K. It's in the introductions they give you, and how hard they work to put you in front of big-money investors. We saw that a couple days ago with the e-mail exchange where PG tried to get Union Square Ventures to invest in AirBnB. Most investors won't even look at you without a personal introduction from someone they trust.