I'm with you on the HR thing - it is inappropriate. Unfortunately, that's how many places handle things like this. Using HR is a way everyone who's really involved can stay nice and clean. Well, except the guy getting the bad news. Being a manager doesn't mean you have nuts.

In my mind, your wanting to learn the lessons from this is one of the bigger pieces here. Was it office politics? Biting off more than you could chew? A communication breakdown somewhere? Some of these things you can do something about, and some of them, nothing.

Keep moving forward, hold your head up, and you'll be better for all this.