It is possible to turn a bike with no hands on the bars, simply by leaning, and that is why some folks will argue that they turn their bikes by shifting their body weight on the bike. Of course, what they don't realize is that the BIKE is turning because of countersteer, or the physics of the rotating wheels and the alignment of the two. A motorcycle wants to go in a straight line, all the time (except at low speeds). If the rider could somehow be lifted off a bike going 40mph, on a perfectly flat, straight road, the bike would continue in a straight line all by itself. It will only fall over when it slows to speeds where the gyroscopic effect of the wheels is negated by gravity.
Understanding countersteering, and practicing it until it becomes something you do without even thinking about it, makes you a better, safer rider.
But, I have come across several people who have been riding for years who will swear that they turn their bike by leaning, and in fact, they do...not a very effective way to steer though. What you can't make them understand is that the bike is countersteering itself when they lean, and leaning in the direction of the curve, if their hands are on the bars, puts pressure on the lower bar whether they are aware of it or not. Countersteering is counterintuitive, thus the name...until a person is conciously aware of it, they really shouldn't be riding.
But most of us already know all this stuff, including effective braking.