Hi,
I have read almost all post about and I am asking myself if that discussion is for discussion only.
StockFish is excellent engine and I do not imagine an analysis of the position in cc game without it. It chooses more different moves then other engines.
SF is GPL and free, so the authors have made a generous gift to the public and have not taken it back as I understand .
If we made a gift to someone we do not have an influence what will happen with it. It can be sold or given...
The prize for that discussed apps is a matter of agreement between seller and client.
Someone prefers to get sth for the symbolical price someone for free.. O.99 $

It is not price to be a serious one for the engine may be it is a price for using the link or the space on the server? More peoples know link to that site then to SF site. Due to that more peoples will get SF.
In one place petrol price is differrent than in other. Is it a legal problem?
Making money from chess programs is being a past when there are so many very good programs for free. It is the true everyone has to accept.
Only selected persons (hobbist) will buy commercial engines to have them in their collections.
Rgds Hood