Well, not so much shocked about, but more by. I KNOW you're supposed to have the third pin there, and it's I guess because if you're leaning on one, and you touch the adjacent game, and one of them doesn't have it's ground plug, the one without the ground plug finds ground through you, and then through the other game. Great.
What I do NOT understand - heh, and most will find shocking as I do - is that a slight touch, say with the hairs of your arm, can create an UNBELIEVABLY uncomfortable sensation, that you don't feel if you just grab both of the games. When I was a kid my grandparents had these old reel to reel tape recorders, and those too had that same sort of shocking feeling - particularly if you touched the microphone to your face by accident. OUCH!
WHY Mr. Professor? WHY do my pinballs shock me when I only brush them and not seem to shock me when I grab them solidly?
-Brian