While Nintendo itself may focus on developing games that are \'family friendly\' most of the time, the variety of games comes from 2nd and 3rd parties.
While you\'ll have games such as Mario at launch, you\'ll also have titles such as Eternal Darkness, Wave Race, and Resident Evil 0. Does anyone want to convince me that games like RE0, RE1, RE4, Turok 4, Eternal Darkness, Too Human, Raven Blade, Perfect Dark 0, Metroid, etc... are for kids (Be my guest)?
The fact is.... the GameCube will appeal to people of all ages. At this point in time you cannot tell how much so or to what extent, but its evident, even in the N64, that this is the case. This also won\'t be another N64, but I believe it will have more variety than the N64 (its already proving to be true).
Nintendo... throughout the N64\'s life has developed games like Mario, Paper Mario, Mario Parties, Zelda: OoT, Zelda: MM, etc... and its likely that you\'ll see these kinds of games come from them in the GameCube\'s lifespan. However, at the same time, you have 2nd parties like Rare, Left Field, Silicon Knights creating games that should appeal to the older gamers.
What one, or even a few developers, think... doesn\'t really matter.