As someone who has gone through YC, this makes perfect sense. My company, along with 15 others in our group, radically changed their idea to the point where it didn't matter what idea we came through the door with. We started out with a Facebook app for sports stuff and ended up as a successful video advertising business. Absolutely zero correlation. PG bet on us in the beginning, not because he loved our idea (it actually was a pretty bad idea), but he saw that my co-founder and I gelled and that we were determined to make whatever damn thing we touched into some form of success.
The other thing to think about is that everyone, i mean everyone has some idea they have thought about which could be a business. If you're the 1% that have never thought of something that could use a change in this world, then the no-idea application probably doesn't apply to you. For the other 99, you can come in with a handful of things that bother you in the world which could be solved by software and YC will more than likely help you pick something they know has a pretty good shot if you are willing to put in the hours.
The other thing to think about is that everyone, i mean everyone has some idea they have thought about which could be a business. If you're the 1% that have never thought of something that could use a change in this world, then the no-idea application probably doesn't apply to you. For the other 99, you can come in with a handful of things that bother you in the world which could be solved by software and YC will more than likely help you pick something they know has a pretty good shot if you are willing to put in the hours.