An interesting read, indeed.
Honestly, I've never perceived the texture to look like denim. I'm wondering if this was something corrected with the Hi Res textures? (never got to play with them) I'm seeing a lot of pics on Google that do in fact look like demin seams, and they look a lot sharper in detail.
I guess my biggest misconception is that the original suits from F1 & 2 appear to be a tight leather, as you mentioned in your blog. I've never read anywhere that the "Fallout 1" suits and the "Fallout 3" suits were different, so just assumed it was leather. And like you mentioned earlier, lots of people have made that connection as well.
In NV, the girl in the vault hotel inside NV makes a comment that they are leather. If your speech skill is high enough your character says something about shining the leather by rubbing it or something. I'm not sure leather would be the best material to use unless they have cows down in those vaults to make more with.