I'm sure you see the difference here in what these two did and the examples you gave. I'd like to add that, maybe it's not kidnapping under the law, but it should be: he is 18, she is 14, AND they crossed state lines. If I remember right they were found in Indiana. That should change everything, why it doesn't in this case is beyond me.
I don't see it as kidnapping. Other laws were broken. Without that, she'd be grounded, sent to her room, and forbidden to see the guy again.