I'm not arguing that it can't be done, just that someone who is over weight and deconditioned is not going to have the stamina to work out enough to make a significant difference in their weight.
How long did it take you to get in the kind of shape to do that?
Yes, you're absolutely correct, but stamina comes with practice. The biggest issue IMHO is motivation: if you don't have it, you're not going to keep exercising for long enough.
Riding 22km once was no problem, and shouldn't be for most healthy people given plenty of time and a working bicycle.
Riding it both ways on the same day took me a couple of weeks. This was coincidentally the point where I noticed weight loss.
Riding both ways three days a week took 2-3 months. (I did it before that, but then was too tired next week.) Note that this was about 7-8 hours a week of exercise, ie. a lot.
Now, about two years later I might be able to ride that kind of a commute five days a week. But my commute is only 15km now (which is a lot easier) so I haven't tried.
How long did it take you to get in the kind of shape to do that?