Before I actually bought a guitar I gave some consideration to both playing right-handed and playing left-handed using a right-handed guitar. They're both really attractive options because they would both allow me to pick up and play pretty much anyone's guitar, as well as the greater breadth of purchasing options. Luckily for me I have a friend who plays guitar and is right-handed, so I was able to try both of these approaches before I actually went out and spent my hard earned dollars on a guitar of my own. Ultimately it boiled down to what felt best for me, and after exploring all of my options I felt that a true left-handed guitar was simply the way to go.
I'll also mention that I used to play the trumpet when I was younger and I played it right-handed. I can still remember trying to play it left-handed initially but because of the nature of the way the instrument is built, I can't imagine that I would have become nearly as good at playing (not that I was incredible, but I was okay) had I not learned the instrument right-handed. I hadn't really considered it until now but I suppose that my years spent playing a trumpet might have some impact on why it feels more natural for me to use my left hand for fretting notes. Working a trumpet valve and fretting a not, while not the same, do share some degree of similarity.
I also think that the guitar, because of the way it's played, presents a greater challenge than pretty much any instrument that I can think of with regard to handedness. In my mind, I'd imagine that because of the way you hold them, instruments like violins or cellos would lend themselves slightly more to being played "off-handed" by a lefty.
Sorry for the long-winded post but I hope it provides some insight for you.