Gee, I hope you don't think I'm being obsessive or anything about this movie. 
...
I don't think this is too off topic as the similarity of his clothes, even twenty years later, shows how consistent - or some might say rigid, he was in his own self image, be that good OR bad.
jackster
No, I for one certainly don't think you're too obsessive!! There are certain other details I am very obsessive about, also. I love all the details -- and obviously Ang Lee did, too -- wanting to make sure the movie reads correctly.
Anyway, I don't know that Ennis's jackets really say too much about him personally. I think it's just that in men's clothes in particular (not city clothes) there is simply a utilitarian element, and styles have no reason to be changed. We might look at jeans as another example. Only in last decades of 1900's did jeans become subject to significant style changes, but basically, men's jeans are men's jeans, and you can still get the plain, basic style. Anyway, the jackets that a working man such as Ennis would wear, the styles would remain the same, when the styles "work" and don't need to be changed. Or denim overalls. Or work boots. Anything like that. (I'm envious of men's clothes -- "Madison Avenue" makes sure that women's clothes change twice or more a year to keep women constantly buying!) Also, even into 80's Ennis might not have access to all sorts of new-style clothes -- he would just go to Sears or his local farm mercantile and get a new jacket to replace the other one after 20 years!
Now who's obsessed, huh?
kathy