Honestly, I don't think this is just specifically a gifted vs non-gifted difference. You mentioned a recent major stressor - divorce... so I would also recommend you look into resources for parents/family helping children with divorce too.
And, no, I don't think even all "modern" parents would consider this normal acceptable behavior... we have not changed that much. Although my kids are not that old, we watch a lot of the kids in our neighborhood (we are in an area with very high density of children) - and seen a lot of parenting "styles". And most parents I know with older kids would not tolerate this behavior without consequences and without serious attempts to get to the root of the kicking/hitting/biting and modifying it so that their children resort to more acceptable ways to handle their anger or disappointment.
