Fair enough, but I'm not sure that NYC would keep me in the house for exercise.

I live in the mountains of Colorado, but will always prefer exercising outdoors, even in winter. I tend to modify my exercise for the time of year and weather. In winter it tends towards running and skiing. Summer is for biking (and more running). I like to have variety of activities (helps to build up a diverse set of strength) and the simplicity of walking out my front door. (Without a monthly fee)

Previous years I've done running in the summer, but I hate it in the winter. Motivation to work out has been a hard enough barrier, so once the air gets too cold to breathe comfortably I'd pretty much stop.

Exercise bike was a game changer last winter in terms of getting me to stick with regular workouts.

New Yorkers just stop at the gym on their way home from work. The net time difference is close to zero. However you also have the opportunity to actually meet other people at a gym.