Rock Band and Guitar Hero, they don't intentionally include the ability for someone else to play along by punching them. For Norway's Morten Skogly, that choice seemed only natural. On his website, you can see a shot-by-shot breakdown of the process necessary to transform something that creates music into something that plays along with music.
In fairness, the entire (ridiculously intricate) process leads to the hilarious video you'll find after the break. You see, rather than strum on the strings of his guitar, the punching gloves (punching him, mind you) approximate a strum for him. That means that every time he pushes a note, he gets punched. It's like penance!