I think that the initial assertion is a bit inaccurate, though. What is a popular route? How about Los Angeles to Sydney. There are three A seats and nine D seats available for Friday's flight. Or LAX-HKG. There is one first class seat but no biz. However, there is the following day.

I agree with the previous posters in that you just deal with it. The tix were bought at a discount with the knowledge that seats are limited. If someone cant deal with the limitations then this isnt a product that suits them. And at the last resort you just take a downgrade. It stinks but again that's the risk one takes.