This, I think, is why people think wider bars are more stable and that they have more control--larger hand movements, larger margin for error.
This sounds correct, but I do think most have little difficulty in riding with their hands on the "tops" at anything but low speed; this position is much more extreme than narrow handlebars. I think it's more about learning curve; even with identical handlebar width, two bikes of varying geometries will feel different and switching to a different geometry bike will require some miles to fine tune one's "control system".