PBA: An old friend of mine pointed this out to me when I was defending the Bracha of “Shelo Asani Isha”. (The “Gam Yesh Lomar”). Personally, even if it is true, it makes no difference, as once Chazal were Mesaken to say the brocha, we say it, no matter the reasoning behind it, just like any other Takanas Chazal which doesn’t fall off just because the reasoning no longer exists. This is the Torah Temmima, please allow the link.
http://www.hebrewbooks.org/pdfpager.aspx?req=14052&st=&pgnum=219
Finally, you have to differentiate between Minhag, Takanos & Halacha. The Halacha is that a woman can not be an Eid or be part of a minyan because the Torah requires males. Period. Takanos like Yichud (2 males vs. 2 females) also do not change due to society. Minhag on the other hand is more ambiguous. It was always the “Minhag” for women not to go to school until Bais Yaakov.