I think I've figured out what sucks so bad about having your coworkers fired.
First, there's survivor's guilt. I'm still here, they aren't. That's not fair.
Second, there's none of the rituals that usually accompany someone terminating employment. Someone quits, and there's a card, and some money, and a meal or beer at the local lunch place. When a coworker is fired, especially a well liked one, the lack of those rituals is really quite jarring.
Of course, I don't know exactly how you'd perform that particular ritual in that circumstance. "Hey, you got fired! Well, good luck finding another job!" Doesn't have quite the same ring as "Good luck in your new position." or "I hope your move goes well."
Well, with any luck, I'll avoid the lack of rituals when my time to leave comes.