Those picks weren't due to his arm strength, they were bad decisions. Manning was straight up fooled by the Falcons hiding extra defensive backs behind LBs. Even if those throws were perfect they would have been picked.
I disagree. They were late or short and didn't have enough zing to get there. I think he may have been fooled to some extent but go look at the replays, at least 2 of the 4 were woefully short being picked off 5-10 yards in front of the receiver. He has never had the strongest arm but the problem has been exacerbated by the fact he is only 80% of what he was.