I can only answer for Europe, but I assume JeffE is going to provide high-quality info for the US anyway.
I saw the most of current postdocs are men.
With some exceptions, this is unfortunately very true across Europe. And not only post-docs. It gets worse the higher "up" you go in hierarchy.
1- Is it because either the women did not apply for postdoc or women's applications couldn't make the CS community or individual faculty members satisfied?
In Vienna, where I did my PhD, we simply received basically no female applications. It was not a question of my professor not being satisfied with the female candidates - in the majority of cases, there simply were none.
2- Is it true that women do not have much interest and hence success in CS than men? or lets say are men -in general- better in CS than women?
I am sure that women are able to do CS just fine. We just "lose" them some time during school. How this happens is a question of reasonably heated debate (gender studies etc.), and I do not feel qualified to answer it competently.
3- Although it is not ethically feasible, is it true to assume that the CS members have tendency to hire men more than women in reality?
This will surely be true for some individuals, but by and large the official university policy in most places is that "equally qualified" female candidates should be hired over male ones, and this actually seems to be the case. In general, as most universities are pretty desperate to increase their quota of females in higher positions, being a top female researcher will actually make it easier for you to get a strong postdoc or junior faculty position in Europe. Edit: I should make clear that the last sentence is based on personal opinion and anecdotal evidence more than anything else.
5- For the women who newly finished PhD, is better to apply for academic research fellows or industry research positions?
Follow your heart. I don't feel gender should play into this decision. Anyway, in Europe there are preciously little industry research positions, so for the most part it's either academic research or industrial practice over here.