No, you aren't exactly getting it. Nobody is paying me to educate, but I feel I have to clarify.
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.