Overall, I know many people who have bought the Nintendo Wii as a casual gaming system because they themselves are casual gamers. However, most of them have maybe bought only 1 or 2 titles because all they really care about Wii Sports. Now while Wii Sports did essentially sell the Wii because the game is so intuitive and easy to pick up and play, it has also stopped many casual Wii players from going out and buying games that they normally would of.
For example, most of my casual gaming friends, turn on the Wii every couple of weeks or so, unlike more hardcore gamers who turn it on at least once a week. And while hardcore gamers get bored with games after a while because they play them more often, casual gamers don't because they don't play the system as often and Wii sports fills there appetite.
So if Nintendo had not included Wii Sports, perhaps casual gamers would of been more open to try out and most likely buy different games. And to be honest there are a lot of lame ports that casual gamers would of picked up played for a while but because of poor gameplay with the Wiimote would of either sold the title bought a new one or bought a new title altogether. Now while you may be thinking people would of just bought Wii Sports anyways instead of buying and trying out all these different titles, when casual gamers are looking at all the games placed on the racks they really don't know which title is best and if they should for instance buy Wii Sports or not compared to a lame port.
Just a thought. I know if Wii Sports hadn't been included in many of my friends Wii's they would of bought more games to find one that they really like.