I never said that you couldn't find plots for three World War II films. Comparing a trilogy to a mini-series like Band of Brothers doesn't work in this case. A television series has a lot more latitude for plot points and character development. You are on a tight leash (for lack of a better term) with the structure of a feature film.
Secondly you are factoring in the comics way too much with your argument. We all know that film adaptions restrain themselves with how much source material they are able to use for the reasons I stated above: plot points, time restraints, etc.
Thirdly, I love the Star Wars trilogy and that is not the same thing as what Marvel Studios is doing and you know it.
I don't know why you bring up Civil War with your argument about Tony. They're introducing the character the start of his career as Iron Man. This has nothing to do with Marvel not wanting to explore the issues that Civil War explored. I don't get what you were trying to say.
Overall having three Captain America movies in theory sounds like a good idea but for the strategy that Marvel Studios has employed with launching their single shared film continuity that culminates with the "Avengers" is just not practical. They want Cap for their film. Dismissing what Marvel wants is not a logical reason for arguing that they should have gone with a trilogy before introducing him in "Avengers 2" or whatever.