Uniform rules have nothing to do with it since they're allowing white vs white in the video game.
There's also a difference between a "throwback game" in which both teams have traditionally worn throwbacks (1994, various thanksgiving games, this year's AFL thing), and the Steelers or Cowboys having their "alternate uniform" being a throwback. And even "alternate" jerseys aren't *always* worn at home... I'd have to look it up, but I'm about 90% sure that the Panthers have worn blue AT Tampa Bay on at least one occasion.
There's no reason not to give us home & away throwbacks, and more of them.