[quote MissX:] "The biological differences between males and females brains are actually so small."

According to Medical Education Online:

"Inferior parietal lobule (IPL): it is a brain region in the cortex, which is significantly larger in men than in women.[...]So, it seems that IPL's size correlates highly with mental mathematical abilities.
http://www.medicaleducationonline.org/index.php?option=com_content&task=..."

Note the use of "highly" and "significantly"!

[quote Gypsy:] "You can't say 90% of people aren't in wheelchairs so therefore we shouldn't build wheelchair ramps."

In the same way women are not excluded from testimony in financial matters nor disqualified. Abilities in each gender is known to Allah and that's why we don't question the Quran or object to the verdicts in it.