Good point. The North American version is the most popular type for the earlier sets like LON, which was without additional letters (i.e. LON-125). The Worldwide, European, Australian, and foreign versions all had their own country code (i.e. LON-EN125 for Worldwide; LON-E125 for European; LON-A125 for Australian; LON-F125 for French; etc.) and are less popular by most collectors.
Regarding your second point, it’s funny how in these earlier sets, only that letter is indeed different, yet the cards themselves were the same. Whereas with newer English sets (whether from the US, Europe, or Australia) are all with EN, even though those can have regional differences with Secret Rares, Ultimate Rares, and Gold Rares in some sets/cards. 
More information about that can (soon) be found in my W.I.P. Yu-Gi-Oh rarity collection guide.
Greetz,
Quuador