I didn't stumble over that much pistoleer characters, maybe that's why.
As for the actual "Sci-Fi Western" - you probably got me wrong on that. I meant the feel of it is very close to what we now know as the "Wild West" - no laws, borderland, people shooting/robbing each other, etc. That's spot on the wild west theme and fallout had/has always a foot standing in it. You may also consider that New Vegas plays in Nevada, where people just tend to wear stuff like that (cowboy hats, etc), even in real life, while the original ones played in California, and (partly) Oregon, Nevada.