In my experience, I have always been asked in the past, like when I used to go to Singapore as a tourist. I'm not sure if every immigration officer asks or checks that though.

I'm not sure if any of you heard about a dummy return ticket. My uncle and aunt who works in the Middle East used to get a dummy return ticket to show to the immigration officer if they haven't booked a return flight. They usually buy these from travel agents when booking their flights. They aren't really booked on that flight but it shows their name and flight details. They pay extra amount for that. Not really sure if it's legal though.