I tend to disagree. I don't necessarily doubt the accuracy of your comments regarding the actual paint finishes found on military hardware. However, several factors combine to make things seem flatter than perhaps the paint actually is.
The effect of scaling tends to reduce the apparent glossiness of a finish. I know when I take a tour of a Navy ship, the gray paint is as you say, semi-gloss, however when I look at it from a distance, it looks flat. You can see the same effect with cars. When one looks at a model from even a foot or two away, the scale viewing distance is actually quite a bit away.
Another factor to consider is weathering. Even a deep gloss paint finish, such as that found on a car, will turn flat when baked in the sun. I think it stands to reason that a semi-gloss would weather to flat much more quickly. Because much of what we model is WWII era when paints were not nearly so UV resistant, I would expect that actual finishes would weather to flat fairly quickly.
As far as weathering and then sealing with semi-gloss, that would sort of go opposite to reality. By that I mean if you have a brand new semi-gloss vehicle, and take it for a spin in the desert so that it can get dusty, the dust wil settle on top of the semi-gloss paint and reduce its glossiness. Think about how much shinier a dirty car becomes after washing it.
If one were building a 1/16 scale tank or 1/8 scale military motorcyle and intending to portray it in an as new condition, perhaps semi-gloss might be most appropriate, otherwise, I still believe flat paints to be generally most approriate, IMHO.