Originally Posted by KingCanute

Perhaps an easier way to think of it without all the airline speak is like this....

You go to a shop and they tell you that one item is $8 but you can have two for $10. So it sounds good, $5 each. Plus you can bring the second one back for a refund if you later decide you don't want it.

But when you take the second one back they tell you the refund is $2 rather than $5. The second item is still fully refundable but because you have now kept only one item you have to pay $8 for that one instead of the net $5 for buying two.

Airline tickets are the same. Single tickets cost more per sector than returns, and on top of any fare difference are the fare rule penalties for changing it. It’s normal business in pretty much any sector I can think of.