Speaking as a cowgirl, neither Bruce Willis nor Brad Pitt are real cowboys. An old Texas cowboy was my surrogate father and there was no better person on the face of this earth. As someone said earlier, it's the person who's wearing the clothes - not the clothes themselves.
I actually think they have more in common:
- they were always armed against danger
- they made their money after much hardship and danger
- they spent their money on women and drink
- they had their own code and way of life that only other cowboys/pirates understood
Oh, and there were plenty of cowboys that were rogues and criminals - who's to say that Billy The Kid and Captain Kidd weren't related?