The other thing that will affect it is the ruling on credit cards, some companies will only allow credit cards based in the country of purchase, which will prevent many people in the first place being able to buy the tickets elsewhere. The other thing is , I believe recently there was some sort of ruling that if you used your credit card for online purchases out of the country then the credit cards would not offer the same level of protection if you do not get what you've paid for or if the airline was to go out of business.