That assumes ZImmerman willingly presented the firearm. Given the incredible amount of restraint the majority of known evidence indicates, I do not believe the gun was intentionally displayed.
I think you can assume that after you are rendered unconscious by your attacker that he will find the gun no matter where you concealed it.
Zimmerman had to assume that the guy who attacked him and was pounding his head into the concrete was not only going to take the gun from him after he was out, but to use it on him to eliminate any potential witness to the attack.
Let me ask you if you had a gun and a guy you didn't know and whom you suspected to be a burglar or other felon had you down on the ground and was bashing your head against the concrete, do you think you would not hesitate to pull out your gun from it's concealed location and use it?
Would you feel OK with the knowledge that if you were knocked out, that the attacker would not find the gun and use it on you because you had not "displayed" it?