Nailak, I often think about that too. But I think that "equal but different" is often used as an excuse to keep women and men in separate spheres.
I reckon that in the olden days there was definitely a need to keep a sexual division of labour and as long as women's sphere was as highly valued as men's I don't see a problem. If you look at some Native American cultures, they had strict divisions (men hunting & warfare, women crops, childcare, building huts) but women's sphere was valued as evidenced in the women's councils that had a say in political affairs.
There does seem to be a lot of evidence however the ideal of separate spheres was heightened during the Victorian times (in the west at least) as a response to feminists' demands for education, which is of course a bit crappy pat on the head ("you do the washing love, you're so much better at it than me!")
So I think that it's safe to say that in Western history, women's roles have been diminished by patriarchy and that "equal but different" has been a sop thrown to women to keep them out of power. I also think the nuclear family set up we have had in the West doesn't help. Men ruled the public domain, women the private, but as the private domain has been increasingly fragmented due to the decline of the extended family, women's lives became isolated and therefore less powerful.