This is an interview, your "customer" is the interviewee, and the answer you are trying to impress on your "customer" is that you are smart, articulate, personable, etc. Even more important, can the candidate look at an obvious question (the quiz) and see the underlying real question (is this candidate outstanding?).

All the things that don't come through on a paper-and-ink resume.

P.S. I've worked with lots of engineers that answer the question that is asked, but never think about what is underlying the question - sometimes the question is wrong. That is the difference between "smart, and gets things done" http://www.joelonsoftware.com/articles/fog0000000073.html and "done, and gets things smart" http://steve-yegge.blogspot.com/2008/06/done-and-gets-things... (a GREAT rant).