The knowledge base article, posted roughly a week and a half ago, doesn't go so far as to say the software is necessary but still advocates "widespread use" of more than one antivirus package to minimize security risks.
By using more than one piece of security software, virus writers can't assume that there will be a particular security suite to bypass, Apple says. In Windows, more advanced viruses already know to look for certain defense suites and will mask themselves or even disable the protection to make their tasks easier.
Apple currently recommends Intego's VirusBarrier X5, McAfee's VirusScan for Mac, and Symantec's Norton Anti-Virus 11.
The posting isn't necessarily a reversal of opinions for Apple, though it does reflect an overall softening of its opinions. While one of the first "Get a Mac" TV spots in 2006 made fun of Windows' susceptibility to viruses and portrayed the Mac as near-immune, the current campaign doesn't mention this point. The company's current FAQ for curious switchers also simply says that Mac OS X "resists most viruses" and doesn't make any blanket statements.
At present, there isn't any immediate cause for a change in Apple strategy. Outside of proofs of concept, few instances exist of widely propagated viruses or other malicious code for the Mac.