Example, I'm watching the Lord of the Rings (BD) and my brother and cousin are as well...except they are playing WoW. For those who don't know what it means to be "playing" WoW it means to be engrossed in the game.
If you are going to watch a movie, watch the movie, if you are going to play a game, play the game.
I completely understand that to some people experiencing the world, happens. Its not something they "do". I'm like that with many things. At any given time, I'm probably thinking about multiple things. To me, thing isn't something I do, its something that happens whether I like it or not. Similarly for them experiencing things is something they can't control. As a result, listening to a movie while playing a game is natural.
It just pisses me off.