Perhaps, but if Doom didn't have such catchy multi-player gameplay would we be seeing Doom 3 making sales for id Software as it is now? Nor it's CEO being able to fund private sub-orbital space ship test flights?

However, I'm not saying that they will MAKE your sales, but if you are going to have a feature in your game, don't pull an Activision and just toss it on top of the game like a sore thumb. The multiple people playing on one computer might be a great feature, but will your players really play your game like that?

However, this is only a meer suggestion or feature that I'd like to have in the game should I play it. Don't take any of this as a 'Golden Rule' or special claim to success.