Ze’evMan: (Don’t know how to make it italics)
“Does the average woman keep her hair covered all the time (meaning while sleeping, showering, etc.?) No. I’d be willing to bet that over 99% of the women in Klal Yisroel today don’t hold to such a standard. So Kimchis’s example is not relevant for most of us.”
I’m not sure exactly why “the average woman” is what sets the standard of where people can reach.
The fact is that women CAN attain these goals. My wife has a separate snoode that she uses for sleeping in, so aside for when she showers or cuts her hair its probably always covered.
The only difference between the gemarah and nowadays that I can see is that in those days the bathhouses were outside the house, so the walls of HER house would not have seen when she bathed.
The whole point of that gemarah in my opinion is to teach exactly the opposite of what you are saying. Yes, it is true that Halacha leaves much leeway for what you can where and when. But the gemarah is teaching that a woman SHOULD strive to the utmost to be as tznius as possible.
In addition the pasuk “hatzneya leches im Hashem elokecha” teaches that ikkur tzniyus is from Hashem, not from other people. So that would mean always not just in public.
Similarly a man can be yotzei limud torah with the mishnah that we say from pea’ah after birchas hatorah. But the mitzvah of talmud torah is a mitzvah tmidiyus and so a man is required to learn every free moment not just the two halachos that someone in the shteibel says after shacharis to grab another kaddish.