Tony brings up an interesting point which I thought all along. Jack is quick to sacrifice other people's lives, well...I wouldn't really say "quick", but his conscience allows it far better when the lives he needs to sacrifice are not his family's - at this point, Kim. I think if Saunder's would have asked for Kim's life instead of Chappelle's, he would have been more desperate to find another way out. And in no way would he have sent Michelle back to Saunders if that was his wife.
I'm not complaining about this, though. I think it's a great character flaw that makes him human at a state where he has to act inhumane during most of the mission. We all know that he won't stop short in sacrificing himself, as in last season when he decided to fly the nuclear bomb out of L.A.