Well certainly that happened but that happens everywhere. The one unifying "theme" of most Western stories is that of frontierism. The United States was unique in that it had acquired all this land and now it was up to rugged individualists to go tame it. Thus for many the frontier was a symbol of freedom, a place to make or break it on your own, with no one else to blame or credit.
Though I agree with the Doc that the West style of Firefly is an affectation, if I had to pick a more "serious" reason for it, I would guess that the imagery of the frontier West matches with Reynolds' desire for personal liberty. Here's a guy who just wants to make a living and be left alone. He doesn't want to be owned and doesn't want to own anyone.
Well, I can understand that. I am no particular fan of westerns, but I don't hate them. There are several westerns which I would call excellent films, as discussed in another thread. So, I don't dislike Firefly just because of western allusions. I loved
Space Truckers, a mixed genre film that is just good, campy, fun.
I think that if we do begin to settle space, there will be many similarities to settling the American west. Maybe too many, if we try to conquer new worlds, and destroy their natural enviroments. But, when we do this, it will be with the current technology, it won't be with oxen and six-shooters. Things will be spartan, but neo-spartan, not paleo-spartan. Also the settlers will either have to pay their own way into space, or get gov or private funding. Either way, you won't see the poor and the homeless going out there, although they may become that way once they get there.
A friend, fellow B5 fan, has the Firefly DVDs. I am planning on watching the real pilot, which I haven't seen. I watched about 4-6 eps, then quit, since it didn't do much for me. I may go see Serenity. But I doubt that I will ever think that Firefly is in the same league with B5.