No its not. It is like asking why are you holding a piece of paper you are writing on with your left handed. IE the pen would be in your left hand and you would hold the paper with your right hand.
You are just holding the phone. The manipulation would be done with the dominant hand. That is why I ask the question. I am right handed and hold the phone in my left hand because I use my right hand to manipulate the screen.
Think about one of your hands being a mouse pad and the other manipulating a mouse. If you were left handed, which hand would manipulate the mouse and which hand would be the mouse pad?
I think you're assuming the poster is using 2 hands to control the device. It's perfectly possible to use one hand, which would be the left, which would bridge 'the gap' as a result. Given that Apple believe a device should fit around the user, and not the other way around, should he be expected to change how he holds his phone? Also, since he could hold the original iPhone, the 3G or the 3GS in exactly the same way and experience no problem, don't you think that points to the conclusion that there's something wrong with the iPhone 4?