But how do you create a non-gendered voice? People will read most voices as one or the other. I suppose you can use something that sounds explicitly robotic, but users are unlikely to prefer that.
There may be reasons to prefer a gender of voice that have nothing to do with roles. For example, I tested both the male and female voices available on my Tom Tom GPS, and found that the female voice was easier to hear because its higher pitch did not get lost as badly in the noise of the car. Only one voice of each gender that had the ability to speak the street names was available (Tom Tom calls it a “computer voice”; it has a phoneme library that is used to build the full vocabulary of street names), so I can’t say whether that conclusion was specific to those two voices or is more generally true.