Japanese Anime does the same thing.
Cowboy Bee bop everybody speaks Japanese. Even in Mexico
The themes that come across in a television series or a movie are going to be the themes that come up in the creative teams culture, so if you are looking at an American writing staff they are going to come up with ideologies of striving for freedom. Where a Japanese writing staff may have a theme of hard work and striving for perfection.
Since a lot of your examples are of the space faring war type movies it makes since that they all have a military or political theme to them. That is what is interesting though. Since the beginning of time stories have had aspects of both, I would hardly say its an American thing.
Then your last point could be covered by How M said it, though i would like to point out that we are not to the point where we have taken the human element from war. and fighting would be incredibly boring without the human component.