It doesn't apply to Zimmerman because when it got to the point that he used deadly force retreat wasn't an option. He was flat on his back with someone on top of him beating the crap out of him. That would constitute self defense in pretty much every state in the union.
I think the question will be how accountable does Zimmerman have to be for creating the situation in which he did feel the need to use his gun.
In much the same way, how accountable would someone be for starting a fight outside a bar, getting beat up, and shooting the guy who was beating him up?
Unless eye witnesses, or phone conversations show up no one will be able to say who provoked who. The inability to prove who provoked who was what I was trying to say with my comment. That's why this thing is a mess. There is no clear bad guy or clear victim.