You're right - but the point is that under the current distribution system, if there was a worm, we would need Apple to release a specific patch for it and wait for people to get it from software update - not the best method for fire control. I have software update set to run weekly, so I wouldn't get it anyway for quite a while. Virus protection systems should catch unknowns more easily as a result of dedicated distribution systems and their inherent design is to look for things that look suspicious.
Am I saying that the worm would be stopped right away? No. Just that it might get caught, quarantined, and squashed a bit more quickly. Should people be running software from those companies? I say that the FUD they produce and performance hit outweighs the inherent security of OS X - so no. But, this POC is a reminder that we aren't invulnerable and we should at least remember that virus protection is out there.