I think it's more luck than anything.
If they're desperate for people, and you're the only person who has applied for the last week, then they'll take you no matter how little experience you have. If they've got a string of applicants, and you *look* (yes, i know, it's unfair) young and inexperienced, they'll probably make a lame excuse up.
I'm currently working in a steakhouse, and when they asked me to "come in for an interview", they actually meant "we need you to work tonight".
I had no experience, no idea what i was doing, fucked up non-stop for the first two nights. But they kept me, and bothered to train me because they had no-one else.
Now that they have enough people they're turning away people with RSAs, baristas certificates, bar certificates, experience doing waitressing etc.