The main difference between NA and Europe prices is what MF alluded to - in NA there is a much wider gap between the cheapest "advance-purchase-fare-war" price and the most expensive "walk-up" price while in Europe the gap seems to be much, much smaller. I like the NA system as it is a great example of the economic theory of "price discrimination" - charging each customer what the consumer is willing to pay etc.

I know I'm belaboring my point, but anyways even through the "average price" might be comparable for NA and Europe, the standard deviation for NA is much, much greater.

To the other extreme is domestic flights in India (and other coutries) where the fare for a given route is fixed regardless of whether you buy a ticket 30 min before or 30 days before.