Well you've still got a trip to Vegas out of it. It's not going JUST for the marriage. I'm sure students have planned trips to Vegas before just to go have fun.
You're right, most people just have sex. Anyone who really does that to justify it is an idiot. Might as well just go for it. But it's college and I wouldn't put it past a few to do it. Kind of a 2-in-1 thing. You get your justification and also a fun trip.