I put it mostly down to market theory. The US is the biggest market and therefore "truest" market. DNW, London Coins, St James, Baldwins and even Spink are limited markets (sorry guys). I'd very much like to know the number of participants that attend each auction, but I have a strong suspicion that Heritage is the biggest for coins in the world by far. I know - painful comment. If anyone knows these figures I'll start collating and comparing ... The other part is about slabbing (that has commoditised the coin business in the US to broaden the market) and so grade number must be high to increase rarity. Hence modern machine made coins get better prices. The US market uses the slabbing population reports to rate rarity. Hmm. Well firstly there are 2 companies with their own population of coins and then not all coins have been stabbed yet. So rarity will decrease as more coins are slabbed. Oops. (Then there's those people who crack them out..not me of course..)