Rafael Nadal was in a similar situation. He is naturally a right-hander, believe it or not. Uncle Toni made him switch to left. Why? Probably because it would be more natural for him to get more spin on the ball lefty. When you have more control of your hand, your wrist is automatically more rigid, like it or not. Dull switched to left hand, allowing him to hit with loose wrist and generate insane amounts of topspin. And we all know Dull's game is based around topspin solely.
Now, left-handers have slightly less control over their dominant hand than right-handers do of their right hand. (In exchange of greater control of the other hand of course). Maybe something on the left side of the brain is responsible for these changes. Maybe not. Whatever. But it is possible that is natural for these lefties (Melzer, Nieminen, Falla, Bellucci, Klizan, Lopez, even Melzer's younger brother) to hit with a looser wrist, thus allowing more spin.
bab was right in pointing out the amount of failure in your post from a scientific point of view since you are trying to "bring" an observation that apparently only you can measure with the naked eye.
Exclude Nadal.........who hit with the most topspin in the game? I mean, revolutions per minute since I want to keep this at the basic "scientific" level without flying into wonderland with obnoxious simplifications. As a matter of FACT......Nadal is not the only player in history that averages around 3200 RPM. Guess who is the other guy? A lefty? Sure, Sergi Bruguera must be a lefty to CONFORM to your observation
Federer is not far behind Nadal and he is another righty. Most of the lefties you mentioned can't even touch Federer's average topspin one day a week; let alone on a regular basis.
Maybe, just maybe what your inept ability to interpret your own observation fails to identify is the TRAJECTORY of the ball.
The bold letters on your post above is yet greater evidence on your inability to understand tennis and the structural level. Take away Nadal spin and what do we got? How about you take away Roger's spin? tell me what you got left
Take away Pete Sampras serve; JMac volleys and Borg's consistency as well while you are at it. Of course I don't debase all these great players solely
on one aspect of their game alone but I definitely understand that Michael Jordan without his athletic ability wouldn't be Michael Jordan...............figured out the rest for yourself. http://www.nytimes.com/interactive/2011/09/01/sports/tennis/Speed-and-Spin-Nadals-Lethal-Forehand.html?_r=0