Maybe up in the north it makes a bigger difference. I'm sure down in the southern US that most people wouldn't have even heard of that.
It really depends what they use to rust-proof it... and since I don't have any kind of experience w/that stuff... I'll just let someone else try to answer. But if it's a brand new beetle I would think you'd be okay for a couple years? Yeah I dunno.
I would say no. I dont even think you would have to worry about it if you lived in a salty area (from the sea or something) ... perhaps maybe if you have huge dents where you can see the metal underneath. *shrug* ...
I do see a lot of Subaru WRX's rusting. Usually from dents like mentioned above. Weird.