without going and looking at the frequency list there are a few slight differences. One that springs to mind cos it has local(to me) significance is ch7 which is simplex in usa and duplex here. But I have yet to have one from over the pond that is not switchable and when we have forgotten to switch over it has made no operating difference. Vhf are s'posed to be type approved for the radio comm agency licencing but they don't ask on the application form what the set is. Customs will be interested with their liason with trading standards as radios should be CE marked to say they comply with electro magnetic compatability regs. Sets sold in states do not need a ce mark as it is european community legislation. Lets face it sets sold in the states may well be going onto an american vessel which is sailing the world and he needs to be able to communicate with his radio wherever he is. What's the difference practically if the set comes over here on an aeroplane and is then fitted as opposed to coming over already fitted and working.
Our best buy was a uniden h/h vhf about 5 years ago. totally waterproof, designed for jet skiers who are going to get wet inevitably, switchable int/usa and fits in lifejacket pocket. Less than $100 at the time and still going strong despite frequent wettings.