halacha theory - Keeping up with "local" standards of modesty and dress - of religious Jews, or of society at large

In dealing with issues relating to Tzeni'uth (modesty) and clothing, a lot depends on "local" standards of dress. For example, the RaMBa"M (here) explains that in places where women do not normally go out with just their hair covered, but with veils as well, they should be sure to wear veils as a matter of Halachah. However, since any deviation in the local standard would be a violation of this principle, it would stand to reason that we ought never to have changed our standard of dress from the time of Sinai. Since that is observably not the case, does this mean that, both in practice and in Halachah, we recognize societal standards in determining how we ought to dress in terms of modesty?