The standard has been expanded to "figures of public interest" or something like that. Zimmerman would fit. Malice is defined differently, basically knowledge of falsity or reckless disregard for truth. NBC is absolutely guilty of that. Your last sentence is where I see it getting tripped up. It's not a bright line. If they had taken words or lines out of his speech then I would say it's a slam dunk. Because his words are played and only the dispatcher's words are edited out, they might get away with it.
I also think he'd have a very difficult time proving damages. The damages in a defamation/libel case are meant to compensate for loss of reputation - i.e. plaintiff can no longer get a job because the defendant said such horrible things about him publicly. I think that there's been so much coverage of this case, and so much of it negative for Zimmerman, that he couldn't possibly prove that any one news channel or program or journalist caused him a libelous reputation.
There's actually a defense to defamation to the effect of "the plaintiff is incapable of being further defamed." I think Zimmerman is what's called a libel-proof plaintiff: http://www.speechandprivacy.com/2011/05/what-is-libel-proof-plaintiff.html
"A claimant is incapable of further defamation–e.g., the claimant's position in the community is so poor that defamation could not do further damage to the plaintiff. Such a claimant could be said to be "libel-proof", since in most jurisdictions, actual damage is an essential element for a libel claim. Essentially, the defense is that the person had such a bad reputation before the libel, that no further damage could possibly have been caused by the making of the statement."