MK: DD!! being LAN enable, seemed so half-baked to me. Mario Kart has always been a popular party game, so Nintendo actually was trying to give people what they want- more people playing at a time, more choas, and more fun. This would have actually worked well if Nintendo's online approach was different.
Most families own more than one TV and for these party situations, it isn't unusual to have a friend own a GameCube (esp. to fulfill the controller requirements, and Mario Kart being the 'must own' that it is, it isn't unusual to have another copy of the game either), so most of the requirements are met. But to come up with multiple broadband adapters? When Nintendo itself refuses to support online gameplay? Mario Kart is good but I'll be damned if I'll sink 40 (X N) more bucks on top of the price of admission to play with 4 (X N) people MK: DD!! once in a blue moon.
I was playing Halo with some friends the other day and we decided to hook up another xbox to have more people playing. The most difficult requirement to fulfill was having enough controllers. That is the way it should be. I shouldn't be immediately discouraged from LAN because I have to hunt down non-inclusive, expensive adapters to network Gamecubes. Nintendo has failed even in their diversion from online gaming.