"FemShep's appeal isn't just about what she is, says BioWare's marketing boss, it's also about what she represents.
. . .
Silverman said that it was "amazing" to be able to connect with fans on a one-to-one basis via social media, adding that it probably wouldn't have been possible a few years ago. As for why FemShep's moment in the sun has been such a long time coming, Silverman said that it would have made it very difficult to market the game effectively had BioWare given equal attention to both versions of Shepard. "When creating a rich sci-fi epic like Mass Effect," he explained. "You need to keep a certain level of consistency so people unfamiliar with the property can clearly identify who the hero is that they get to become ... had we released images showcasing both a male and female Shepard, people wouldn't be able to identify who the hero was or what was going on." "
Read it all
here.
I'm happy Bioware finally seems to realize that fans want FemShep to have some more attention. I still feel their reason why they've been holding out on showcasing her earlier doesn't sit right with me.
EDIT: Late update, but here's another article that seems to be taken from the same interview.
Loving FemShep: BioWare’s first lady finally steps forward.
From interview:
"But Silverman revealed that only 13 percent of Mass Effect players use the default Commander Shepard: the remaining 83 percent customise their hero, changing class, abilities, appearance - and gender. Overall, 18 percent of everyone who plays Mass Effect plays it with a female character,” Silverman said."