Yes, Macs are plagued with as many (and sometimes more) vulnerabilities as other operating systems. These are the doors attackers use to exploit our systems, and Macs are far from invulnerable. But the truth is that in the real world, Macs suffer from far fewer compromises. This is the difference between security and safety. A highly secure home in a bad neighborhood is still more likely to be robbed than a less secure home in a safer area. Mac market share is probably an important reason here, as is the history of the platform, the focus of the bad guys, and a host of other factors
While I disagree with the first bit about the number of vulnerabilities, Rich Mogull is dead-on about the difference between safety and security.