The rule book got in the way on this one. Because one of the officials called it a touchdown on the field, the head official that reviewed the replay could not overturn possession. Since the ball was clearly caught inbounds, they couldn't call it a incomplete pass either. The only call they could make at that point was touchdown due to a technicality. At least that is the understanding I got from listening to the referee they had explaining things on the post game show.
That said, he also pointed out that Jennings was the one who appeared to have possession. I agree that it should have been an interception. What should have happened is the referees should have huddled together and established who had possession first, then made a ruling. Doing this could have provented the missed call.
What worries me also, I think had this game been in Green Bay it would have been called an interception. I think the refs gave the Seahawks a homefield advantage.
What makes things even worse is that the NFL and the real refs are fighting over a $500 dollar a game raise and healthcare benefits ($10 million over 10 years).