I've decided that this really isn't buying at all. I'm giving them the extra money. The free ticket is theirs and they could use it if they want to. They never will of course (only because they live in India and never fly except rare visit to US), and I'm sure if I ask to use it they will agree. As long as it is their choice and not an obligation, then it is not buying.

It's not really any different than my parents paying for my tickets for the last twenty years. If they need a FF ticket, I will certainly give it to them although I am under no legal obligation.