Query letters versus resumes

Here's a copy of an email message I received from an aspiring best-selling author, a man who has written his first novel.

Tell me why applying for representation from an agent is any different from applying for a job. For a job you send out 20 or 30 resumes, and with one or more replies you complete the applications and go for the interviews. Whoever picks you first, well, usually you take the first job that comes along.
 
Tell me why a literary agent is any different; you send out 20 or 30 query letters and whoever comes along first you jump on it.
I know I'm naive, but what else is new.

Can anyone tell me how to answer that?

Also, I know the stock answer; but in this day and age, when snagging an agent, yet alone a publisher, is getting harder and harder, should we play by their rules?