Being a fan of Chessexplained on youtube, I recently started looking at the Nimzo/Bogo, going for the dark-squared centre with d6/e5.  I was thinking of buying his Nimzo/Bogo book for more detail, but then I got to wondering, is there any reason to prefer a dark-squared Nimzo/Bogo repertoire to the Old Indian, where you get basically the same pawn structure without even giving up the bishop pair?