robots.txt is a suggestion, not a rule. It's a service to crawlers to help them avoid wasting time. Using robots.txt as a security measure is like trying to stop a foreign invader with a "road closed" sign.

Edit: this is obviously assuming they literally meant robots.txt, but from a qyick skim of the site, it doesn't look like that was mentioned at least. I guess you meant it metaphorically :P

Why should they not? So does my browser when I ask it to open a website.