There is NO lean when you're using different hands. I have made a little diagram to try to explain what the different hand positions do. The black X represents your crosshair, the circles represent the flight path of of the 'perfect' paintball leaving your marker(in other words an autococker with steel barrel). You'll notice that dependsing on the position of the gun in your hand, it starts from a left, centre, or right offset as it travels to the target. This provides a slight advantage in very minimal circumstances. If it makes any difference, myself nor any other eR33t members to my knowledge switch between the hand positions while we're matching to create better angles on shots. I really think you're blowing this whole "leaning" thing way out of proportions.
Let me know if I've left anything unclear.
As for the leaning forward, when you currently look down, you're technically looking through viewing the view from the immediate centre of your brain, through your body and right between your feet. What jitspoe is suggesting is that this be changed create a more realistic view angle of what a human would be seeing when looking forward. It would also give players the ability to lean out of windows to shoot people just in front of you, on the ground. Really neat idea.