Hmm, I never stopped to think about why. It is just something I have always noted, at multiple institutions during different levels of my training (as a surgical orderly in undergrad, as a med student doing rotations, and now as a resident) Dont get me wrong, my best friend is a gen surg resident and i know plenty of cool, easy going General surg attendings and residents, plus i also have met some ortho res and attendings that are serious assholes. As far as if people go into a specialty b/c of their personality, or the specialty shapes their personality, i think it is a little of both and varies depending on the person/situation.
It is tough to judge though since your experience in a specialty (any specialty) will be different than mine or the next guys b/c we went to different schools and had different experiences. The sugery residents where i am now are TOTALLY different than where i went to med school.
Good luck deciding