>It's about half an hour a day, that's all you really need. True, if you can't spare half an hour, then you've got greater issues.

Unless you don't have a car, or live in a congested city, or live outside the city, in which case it can be half an hour of commuting time before you get your half hour of exercise. It's also ~$60 a month, which not everyone can spare. Your statement also assumes people aren't working two jobs, and aren't working shift work (or have access to a 24h gym, which not everyone does).