I think this really boils down to individual needs and motivation. Some people, like myself, need to get out of the house, whether it's to the gym or on my bike, to feel like they are committing to a workout. Others are content to do it at home. I'm not going to criticize anyone for employing a completely different strategy than I am. If it gets you off the couch and putting out an effort, it's all good.
Sweat is a terrible measure of calories burned, btw. I know there are days when I do the exact same routine that left me dripping two days before, and stay relatively dry. I suspect it's a better measure of ambient temperature and humidity.
I'm also not really thrilled with this idea of labeling people as "fit" or "not fit" as if those are absolute terms. One of my favorite people to talk to at the gym is a guy in a wheelchair with barely any use of his legs. A few times a week, he gets himself on an elliptical machine and does about 15 minutes working both his arms and legs. Just getting himself on that machine is a huge accomplishment, and I'd put that up against 10 perfect pull-ups any day.