As much as Intego wants to present the state of malware on the Mac, the truth is that even Intego works pretty much like any other AV engine which tries to detect malware based on its signature or heuristics (behavioral), that they receive either from someone sending them a sample or collected with their honeypots around the world.
The bots/trojans/RATs that are written for specific targets, do not have a signature, thus, are undetected. Then it becomes obvious that Antivirus solutions are not enough. You also need to control the apps that are reverse connecting (phone home), with products like (Little Snitch).
What they don't address are the vulnerabilities that exists in every day applications, which subject to a stack buffer overflow, will execute code in memory with the same level of permissions as the application/daemon that is running. Antivirus doesn't provide any protection for exploits in software.
On a side note, Intego mentions a "crack" for CS4 which is actually a Trojan, but doesn't mention that Adobe's own CS4 install tries to phone home.