Of course, the chief executive of an antivirus company isn't necessarily going to target a new market because his product is necessary in that market, but merely because there's an opportunity to make money there. I'm not currently aware of any Trojans, Worms, or Viruses that have had any substantial impact on the Mac platform, though non-OS-oriented exploits such as phishing attacks certainly run rampant among Mac users just as they do among mainstream computer users.
That's why AVG's new software for the Mac isn't a virus scanner, but rather is a "link scanner," which appears to compare any links you click on to a blacklist of known malware sources. It would be a useful service for people who are indiscriminate about what they download or fill out online. I'd be curious to compare this service to the malware blacklist feature that's built into Google Chrome.
Currently, this product will be free, and AVG works on the "freemium" model, offering advanced versions of its tools for a fee. I wonder what they think Mac users would eventually upgrade to?