The point about how many modern airliners are designed to operate with only two engines (at ETOPS standards for RATs, APUs etc), and how far they can be (up to three hours, single-engine!) from a suitable alternate, is interesting. But if the 747 suffers a problem with another engine, then it might not be a pleasant day for the flightcrew. How high can they cruise near maximum weight on two engines in August during a diversion over desert mountains? How about from over Greenland?
I just read somewhere that BA, or a European airline must pay quite a chunk of money (i.e. $100,000 ?), if a flight returns to its departure airport. It looked like this is in addition to extra operating costs.