I think they delight in American deaths for a number of reasons:
1. They're American soldiers, and they hate America, so they're happy Americans are dead.
2. They think the deaths are something they can milk for political advantage. Makes 'em even happier.
3. They're probably "white boys" from the south, country boys, and of course, that means they're probably heterosexual, and worse, probably Christians, and even more repulsive to them, they actually have testosterone and aren't afraid to put it on display. Nothing is more repulsive to the mean-faced, clipped hair dykes, the man haters, the anti-Christian and "Get Whitey" crowd.
I honestly believe that the left is gleeful that American soldiers are dying, for all the above reasons.
You are exactly right. I have no doubt that, say, Tom Daschole gets an erection every time he learns of another American killed in Iraq.