This is just a hunch, but could there be a loophole possible with those promotions where you get a discount, but only if you own another related game? Maybe devs can just add discount for owning a free game and fake a permanent discount that way?
But as OP already said, we’d need a dev who’s already published a game to confirm these kind of theories.
Edit: This comment is probably right and it’s just an automatically applied bundle discount, but there’s a bug in the Wishlist where it shows the combined price of the bundled games. If that’s the case then Valve should really fix this ASAP, since it probably falls under false advertising in some countries, even if it’s a bug.