You look at lists of the rarest, most valuable, most traded, most in demand coins, over 90% of them are American coins. Why is this?
Sure you have your odd Dubloon here and Roman coin there which have a high intrisic value (i.e. headed for a museum), but mostly apart from that, the only coins traded are American.
Go to eBay and check it out. And if you're not convinced, go to eBay's Euro or other sites and search- all you see are American coins.
What makes American coins so special???