Not as common? There isn't a single male voice over for anything Advent....now to be fair, there isn't a single female voice over for anything TEC, though they do at least have 1 player graphic for TEC that is female...
I would say the choice to use only male voice overs was purely for that grizzled, hard core soldier effect...but then they threw in the creepy hoshiko voice, so I'm thinking its because the TEC has no women...at all....like, anywhere...in fact, they probably did have women until they cast them off into the depths of space 1000 years ago for doing creepy woman things, whatever that is...and then those women, rightly pissed about the whole affair, came back with horrid white dresses and hairdos (pretty ships though) styling themselves as the "Advent" and "Unity" and what not...
Might also explain why the Vasari seemingly have only male voices...they probably did the same damn thing 10,000 years ago, and now the Vasari Amazonians have them on the run...
In all seriousness my guess is that the single gender choice for graphics and voice overs was for "effect"...the Advent just wouldn't have the same "feel" if some girly man tried to mimic the creepy, seething Advent voices or tout his long white man robes...and I don't even want to know what a Vasari female might sound like...
Still puzzled by the Hoshiko voice over...I mean, if there are men in Advent society (which allegedly there are), I'd bet they'd sound like that....