[airhead]

As far as AA goes, tickets are sold accordingly to fares. Each flight has roughly somewhere between 10 - 20 fares. Usually the cheaper ones are bought off by the discount agencies such as Cheaptickets.com. And the fare prices are priced accordingly to market shares. The demand to fly from x to z will usually be different than flying from z to x. Times of the day and days of the week play a critical role. The more fares are sold, the higher the subsequent price will be. The value difference in currency is exchanged by the various banks conducting the transaction.

One should be able to book from another country if the airline does fly from that country and the bank of origin allows it. Their has to be an agreement with the booking agency to do this. A dot uk site may not honor an American credit card or booking since an agreement with the travel agency may not exist.