Lacking empathy doesn't mean we lack emotions. The problems we aspies have is that we cannot TELL deep emotions just by looking into other people's faces. For instance, if two of my friends have had a row and are mad at each other, no matter how much they ignore each other or how cold they act when the other one's around, I won't notice.
But it they tell me they've had a row and they're mad about it (or if they feel sorry, or lonely) I will understand, even though I wasn't able to tell in the first place.