Man, you gotta go into pickin up a chick in stealth mode, and askin if she has a boyfriend isn't stealth mode.
Besides, who cares if she does anyway? Chicks pretty much go from guy to guy without much time between. Even if she does have a boyfriend it doesn't mean she's not looking for something better, so don't even ask.
As for katie's pick up line, it's funny and all but in most cases it's only going to get you someone to talk to for a few minutes. Most women want to feel like shit just happened spontaneously and they got swept off their feet by some really cool guy. By the time they're fucking they want to feel like they somehow lost themselves and wound up getting fucked by accident. That way they can rationalize it as not their fault. So, announcing off the bat that you're going to be hitting on her puts her on the spot right away. They really don't want to feel like they're some slut that can get picked up in a bar. (Yeah, yeah there are exceptions, but if they weren't exceptions we wouldn't have to work so hard at getting laid, would we?)
Anyway, that's why pickup lines are shitty. They put too much pressure on the girl, and if she ends up fucking you she'll feel like a slut about it and she's not gonna let that happen. You've preemptively shot yourself down.