I'm gonna be as concise as possible here. I'm not good at that though. I've never been to a strip club, but I know guys who have, and I have had the urge to before, just never actually have done so.
There's no touching. You get kicked out for touching the girls (at least at any decent, i.e. licensed place). As for them touching you that's entirely up to their own discretion, but usually doesn't happen much either.
What's the big deal? Well guys are very visual, and very visceral. (in other words we respond to things that are immediate, intense thrills, thus why guys like action movies, there's no subtlety about it, just immediate, superficial emotional response). As that applies to strippers, there's something about being able to see a naked woman for a bit of money is appealing.
As for turning you on in ways a girlfriend can't, it sounds like you're worrying about that too much or that you're threatened by it when you really need not be. What that means really is just that it's a cheap thrill. It's "dirty". Your girlfriend can be as dirty and slutty as she wants, but it's still essentially imitated dirtiness, cause essentially you're still in a relationship with this person, and no one REALLY wants to think of their girlfriend as a cheap slut or anything like that. It's not that you're not good enough in bed, or you're not attractive enough (some strippers really aren't that great looking anyways), or that strippers can do things you can't. It's mostly just a situational thing. It's not the stripper herself as a person, it's the fact that she is a stripper, that it's a strip club, that you paid to see her naked... it's a cheap, dirty little thrill.
So basically, no, wanting to see a stripper doesn't mean that they're better than your girlfriend... or that they have a betterbody than your girlfriend... at all. Seriously, even some guys who have the hottest girlfriends in the world will still like to see strippers. It's all just about the dirty thrill of it all. The way I like to put it is that strippers and porn are to guys as smut nd romance novels are to women. Women get annoyed if a guy was threatened by a character in one such novel because it's a fictitous character and we shouldn't be threatened by them. Well that's how guys think of porn stars and strippers, they're not really "real" people to us, so much as they are just superficial characters whose appeal is in the simple, dirty thrill.
I hope this is helpful.