Well, imo the 360 isnt popular enough to be deemed a fad.  but it would also need only limited appeal.(as opposed to lasting)  It has a fairly diverse library of respectable games, meaning there should be some things to promote lasting appeal among the people who purchase it. 

i could probably find them fairly easily by using a search engine. 

Most of society falls into the severe category sadly.  results are likely to be minor.

a couple of keystrokes and i find

a video demonstrating some yoga for beginners
http://www.youtube.com/watch?v=LKl1JzF4EQU

another couple strokes and i find a site about yoga that seems fairly comprehensive
www.thesecretsofyoga.com

 Does the site provides you with some kind of interaction??? or is just pure videos???

One of factor for the success is the interaction, yes you are doing yoga, but the wii board + software provides enough feedback to keep you in... yes they are videos, but is any of them more interactive than wii-fit???

Baby steps my friend, baby steps ...

I have worked out for about 15 years and I have noticed that so many people rush in with all the 'motivation' in the world, worked out for 2 to 3 weeks, and then quit because working out did not fit their lifestyle. Something simple like Wii Fit that can be done in people's homes for 20 minutes can be worked into a lot more people's lifestlye, and in association with even minor dietary changes can drastically change a person's body ... Basically, if you convince someone to put on 3 pounds of muscle (180 additional calories burned per day), to cut their diet by 150 calories per day, and to burn 150 additional calories per day through excercize a person can lose 1 pound per week for quite a while.

Why don't you buy WiiFit, try it out, and then sue Nintendo because it's causing your legs to hurt or something.

the yoga site seemed to be information, videos and photos.  i will concede that that particular site was likely less interactive than wiifit.

but as a reubttal...does wiifit provide as much information as the site?  or perhaps other yoga sites.  i only spent only 10 seconds looking for a site.

We need Super Gold's Gym: Wii Edition. LOL (Yoga is more of a woman's thing)  Oh and the OP is right about the BMI indication thing.  You can still weigh the same with BMI weightwise but build muscle at the same time to equivalate.

the gym is a fad

but seriously, its selling well in Japan after all these months, I sometimes see wii fit staying in the top 5 for many weeks.

Thats the point, more people will look for something easy than can correct you on the fly rather than  pure detailed manual on the web...