asdvertising regs differ wildly in the US and UK, you have to be able 'to prove any and all claims and comparissons' made in UK adverts, otherwise the ASA can pull them with as little as one complaint.

in the US its way different, broadly speaking you can say pretty much what you like as long as it isn't slanderous or libelous, their is very little in the way of advertising consumer protection law in the US, but then again they'll sue your ass just for looking at them over there.