I've always thought about this, and I personally came to my own opinion that the reason why Femshep is so cool is that whether or not you go paragon or renegade she doesn't come off as the typical stalwart hero of the galaxy like the WASM the man on the game cover is.
Her actions and movements being the product of Bioware laziness seem to be typically male, but Jennifer Hale also turns it into something feminine at the same time. So she still is
woman instead of being a total man trapped in a woman's body
I get the vibe that femshep's popularity was in no way planned. It just happened to be a combination that fit just right.
Although now that I listened to Yahtzee's review of the games I can't shake the fact that yes, indeed, they do seem to have a BioWare Face. >:
It struck me when in LotSB femshep screams "LIARA'S IN THERE" all anguished-like and her face is exactly the same as it was when she was being asked to hack terminals for
Liara that domineering bitch