To recap the above, countersteering and leaning are essentially the same thing. The people that think they're leaning to turn are using countersteering to get there, they just don't know it. Search the web for countersteering and you'll find tons of stuff on how this works via the contact patch, gyroscopic precession & more. If you're into physics its pretty interesting.
Originally Posted by CATZ
Well, that seems to make sense.
Now, let's muddy the waters a bit more. What happens on a trike? I believe on a rigid trike, you would have to "steer" it .. in the direction of the turn. (much like a childs tricycle)
Now, if we were to allow the front wheel and rider to lean, independent of the rear wheels (articulate, I think), would the steering be like a conventional bike or a tricycle?
You got it. If the trike is rigid, it'll steer like a car - i.e. you point the steering tire(s) in the direction you want to go. This is typically a pretty unstable setup. If you can lean the turning wheel(s) you'll get better performance, particularly if you can lean the payload too (i.e. rider) - its helpful to move the c.g. towards the inside of the turn to reduce the risk of tipping. Same reason you lean on a two-wheeler - beyond a certain speed, if you don't move your c.g., you're not going to stay on the bike.