User blog comment:Shifter77/Shepard's mom WHAT!?/@comment-4980393-20120407084759/@comment-4618888-20120407124937

I don't remember when the e-mail shows up (or if it even shows up at all for PS3 players), but you might also hear a news story while on Illium/the Citadel about Hannah Shepard turning down a promotion to admiral.

I suspect that they didn't want to show too much favoritism to one background over another, and that's why family isn't mentioned much (since the other 2 backgrounds have no immediate family left).