The experiment was performed in Japan...
That explains at least part of the sex difference right there. Japanese cultural attitudes about assertive women are justifiably notorious.
Up voted, however this is pointing out the obvious.
I think the real awkwardness is that people assume that a sex difference would exist even if the experiment was repeated in say Sweden. Sure there is still a cultural factor even there but I think most people here have a hunch a small tendency in this direction would exist in any culture even if it was masked by other factors.
I'll go out on a limb and say that perhaps women are more conscious of what other people think of them than men. Thus they tend to conform in behaviour to expectations a bit more.
T...
A new variation on the Asch conformity experiment was recently published. The experiment was performed in Japan and used polarizing glasses to show different lines to different people in the same room, so that the subjects had to disagree with others they actually knew, and who genuinely believed that they were answering correctly. The study found that women conformed by giving a wrong answer about a third of the time, but men did not.
Learned about this via Ben Goldacre's blog.