Yeah, it actually started with Pokemon Platinum. The PAL version of the game had the Voltorb game instead of slot machines, I guess Nintendo didn't want to make different versions for North America and PAL regions. The Japanese version still has the Voltorb game. What I usually do is only pick the rows/columns with no Voltorbs, then I quit and take whatever coins I got. I usually get 3-9 coins each time I play this way, hence why I will hate winning 9,999 coins (I won't waster time trying to win enough coins for TM's, but this is the only way to get Porygon).
If you don't mind, I would like to evolve my Slowpoke into Slowking (which, as you probably know, happens by being traded while holding a King's Rock).