It's kind of weird. Only military shit bothers me like that in movies.
When people drive cars without looking at the road, having a full 30 minute conversation on a road they never have to turn on, it doesn't bother me. I drive 90 miles a day for work, so you think I'd automatically zone in on those inconsistencies. But it doesn't bother me.
But if I see somebody firing from the hip laying waste to everything or something similar it bothers the shit out of me.
As has been said, the dos looking system in Alien doesn't bother me. But most of the Marines tactics/gear does in Aliens. But then most military portrayals in movies do. I think maybe its when you have a physical investment into something you see it different. I often think about Aliens, if Aliens was actually done tactically. But I will also give Aliens props for breaking the "every grunt is the same guy," cliche. Aliens at least attempted to tell their marines apart bit giving them differing, if flat personalities. Not saying they are deep and interesting, just nobody usually confuses Frost with Hicks.
Not always the case in other movies where grunt a could be also playing grunt c, and nobody knows or cares.