I am finding this conversation very interesting!
As a right-handed person, I tend to hold my phone (even a standard desk or wall phone handset) in my left hand in order to leave my right/dominant hand free for note taking and other tasks and, in the case of a smartphone, free to interact with the screen. In fact, I would go so far as to say that I find holding the phone (any phone) in my right hand to very uncomfortable and unwieldy.
At any rate, a good case can resolve the volume button issue, regardless of in which hand you hold the phone; a typical case requires significantly more force to activate the buttons as compared to naked or, like some older Seidio models, surround the buttons with a cutout which makes accidental activation very unlikely.