A person (male or female) should look appropriately PRESENTABLE when leaving the house, yes. But, no, it is not a woman's "duty" to look pretty at all times.
I *like* when my girl can be comfortable around me, and doesn't feel like she needs to dress up and put in an hour of hair and makeup before she can watch a movie on the couch or whatever. That doesn't mean that same look is appropriate for going out to dinner or whatever, of course.
Really, though, it is women, more than men, who still carry these expectations. It's not the 1950s anymore, and men know it, but in some cases, women haven't gotten the message. Part of that is because their parents were brought up with 50's values, and have turned around and passed those on to their kids, without making appropriate and necessary changes that reflect the HUGE social changes that have happened in the last 50 years.
Don't get me wrong here; I love a pretty girl (who doesn't?), and a trip to any Walmart will show you that it's easily possible to go too far to the other extreme, but there's a middle ground that I think is the right place to be.