I recently added a for LOTP. My motivation was merely because I spend alot of time watching them in films, as well as watching the entire film again with the audio commentary on, go figure.
But more interesting was the response, there are people out there who are actually genuinely interested in how games are made, and getting a look at behind the scenes. Personally I'd be willing to pay an extra few bucks to buy a special version of a game, if it came packed with 'a making of' feature, hell it's not like it's hard to implement.
Maybe this could be a new trend for games?