To me, something is lost when you add guns. I'm not sure what you would call it. There's something awesome about a good sword fight where skill and balls come into play. Magic gives fantasy, or high fantasy a kind of flavor and mystique thats not found in modern settings. Together, they fit quite nicely. When one person whips out a sword or casts a spell, and the other pulls out a gun and busts a cap in their opponent's ass, that just ruins it for me. At that point, it is no longer fantasy/high fantasy...
Hell, we could introduce 10 gallon hats, cowboy boots, lassos, revolvers... Oooh! we could even have shoot outs.. where two players start out back to back, take 20 paces, then turn and fire at each other. Add in a gold rush, poker cards, a piano with some Ho in fishnets and a frilly hat sitting on top while its played ... sounds like another genre right? But it COULD be done... so why not?
Just because you COULD does not necessarily mean you SHOULD.