With respect, you are hiding the ball. Those two terms are not synonymous. Some users can experience an endorphin flood from achievement, not merely excitement

With respect, you are hiding the ball. Those two terms are not synonymous. Some users can experience an endorphin flood from achievement, not merely excitement through play, which is probably more analogous to "fun". What these designers have learned to do, however, is establish through the game's ephemera (art, sound, animation, number-go-up etc.) a direct connection between endorphins as achievement and spending money. You spend money, you get the hit. It's a straight line. And that, yes, I will call "downright evil", because it is exploitative abuse of the human firmware for mere profit. Developers of slot machines are excoriated for the same thing; there's no reason that virtual ones are any better.