I have tens of thousands of dollars worth of unused tickets, so I know what you mean. But would anybody want to buy a ticket and not use it intentionally? Presumably this would be to help you reach a status level, or gain an award, both of which would cost the airlines something, so they make you fly.
I disagre with Beckles. Who would pay $800 to get a "free" ticket on SW?
I also disagree with cordelli. The airlines want to reward for revenue contributed. The programs are in place to maximize revenue in a competitive environment, period. Some of the programs are changing to reflect the emphasis on revenue.
Of course you can buy miles at any time, but it is not very cost effective.
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United UGS, 1K, Million Mile Flyer
Hyatt Lifetime Diamond
Starwood Platimun