The non-call on Stevens fumble actually helped the Steelers; they would have got the ball inside the 20; as it was, they got a little better field position after the ensuing punt.
I have seen that happen before in only a few games, don't think it happened here. I think the Hawks were the better team but just did not finish. They really didn't. They lost the game themselves by poor plays....two missed FG's, and the missed touchdown by the receiver at the end of the first half.
Bad timing by the Hawks themselves, not bad referees.