do you often give $1 to your local supermarket and get $500 in change?
I saw an episode of extreme couponing where the person bought about $800 of groceries and got $57 back. But that's not his point. Like i said earlier typically people are getting miles because they paid for them, in other words they are priced in. You buy a product for $100 and you get 100 miles the merchant on average would have reduced the cost of his products if he didn't have to compensate for transaction fees etc.
It's probably more like returning an empty soda can/bottle.
The costs of airline tickets already reflect the fact that travelers will earn free flights.
So when you buy something and receive miles it's like getting change back because it's already reflected in the amount you paid. At least that's how I understand that comment, and from what I understand it's coming from someone who understands miles as well if not better than anyone else on this forum.
I think it was a great issue to bring up, and it shows that there are still shivim ponim latorah!