Answer :

Sorry, I don't have the definitive answer and I don't believe anyone really does because in the end I don't think it comes down to countries but rather which airline you are flying with. I've had this problem flying into several Asian countries-Thailand and the Philippines spring to mind. Sometimes its ok to fly in on a single sometimes not. I believe that some airlines are held responsible if you overstay your visa and/or don't have enough money to get the hell out of their country!- that's what I was told by airline staff- and so insist on a ticket showing that you can leave the country. Boat or train won't do, oh no, it has to be plane. (Quite bizarre really when in Thailand and Malaysia's case you can enter or leave by train no questions asked)

The best policy is to check with your airline as they will ultimately be the ones who decide whether you get on the plane or not. Its very unlikely you'll have any trouble at the other end as again the airline is held responsible.
If your airline says you need a ticket out of the country then I suppose the best thing to do (it's what I did anyway) is to buy the cheapest ticket out available. Best not to try and do this at the airport as, as a friend of mine found out, its often not the cheapest place to find ticket