My same thoughts here:
It seems that those who would get bitten (even if a minor survivable bite), would get a fever from basically contracting the virus and die as a result.
So if it's airborne and everyone is infected, why doesn't everyone get a fever and die?
Maybe when you get bitten you get some extra infection or something that you don't get in the airborne strand. I can't really think of any other explanation.
EDIT: I also said this a few pages back, but it was in spoiler tags:
So they all got infected by the virus via the air? It's airborne. They then must be killed by unsurvivable means such as a gunshot to the heart or zombies eating them alive, since the virus cannot kill them if they already have it. All it does is bring them back as walkers.
But wouldn't some things on the show contradict this? Jim was bitten in the stomach in season 1, it appeared he died from the fever and literal infection of the virus, since it kills you once you contract it. But if they already have the virus, then a bite in the stomach like Jim had should have been survivable and Jim would still be alive today.
The classic scenario is: you get bitten and you die. The virus is the reason.
But what your theory says is: You get bitten and you can survive. the virus is irrelevant unless you die.