Most of the 360's software lineup is about as attractive to me as Carnival games. I doubt I'm alone in this. All the games are bleeding into each other, without any heart, identity or daring. It reminds me of the 90s when there was a gajillion X-men comics and spinoffs that were mindless action and horrible melodrama.
Wii Fit though is something totally different. It's the merging of videogame into lifestyle, but not the lazy gamer lifestyle. People who love it aren't exactly a part of the clubhouse mentality that permeates through comics, Sci-Fi and videogames. What it represents is something that goes back quite a ways, as Pong and Atari were public and social gatherings. Rock Band is this to a much larger extent, but Wii Fit works into this realm as well.
It's sad I feel I should apologize for applying historical and critical thinking to videogames. I've been studying other medias that have had to prove their worth, and only Detective Fiction had the same phenomena of people within the fanbase wanting to hold the media back.
Pong was introduced at bars. It was a social game and the heavily 15-30 male establishment hadn't been put in place yet. Women were actually seen at being somewhat better at the game at the time. The atmosphere we now live in with videogames wasn't there. Atari 2600 was advertised as a social, active, family event. The age and gender range depicted in early ads was greater than what videogames came to be in the late 90s. In the essence of play, there has often been a social, active atmosphere to it, but one defined by the magic circle of play. Physical activity within play exists from before videogames, then is a part of videogames in arcade machines, moves on to things like US Track n Field and DDR, and now with Wii Fit.
So, the point is, that Wii Fit is no new gimmick. It's just part of a pre-existing lineage that was forgotten as games moved into the clubhouse mentality. (If you want me to go over that 'clubhouse' menaltiy, the idea of comic shops, D&D dens and boys playrooms, then I can as well.) The thing is that Wii Fit users and buyers aren't being sold a gimmick. They are getting what they want and its something totally different than Prototype. It is a game that works within a pre-existing social atmosphere. Rock Band as well works into this, as does Guitar Hero. These are games you can play in front of others and it invites them into the magic circle of play. If you plop down Prototype in the middle of a party then people will find it an isolating experience, and the party moves on outside of it. Active, social games avoid this by being not just spectacles on screen but spectacles in how they are played. It's the very difference between watching someone play a digital simulation of tag on a TV that has only one interface versus seeing people on the playground playing tag in an open space.
There is also the fact that it fits certain lifestyles better. The lifestyles that have less time to play, or are those looking to be more active but are interested in the idea of making a game of it, but this too harkens back to playground recess exercise. It's just a higher tech, adult version.