First of all, let's put this in perspective. Take a look at the top right corner of that site: "Windows Network & .NET Magazine".
This spin is almost as amusing as the Redmond claim that "we're not coding anything new for a month so we can concentrate on 'security'". One whole month? Wow.
SecurityFocus now warns that the data upon which these assumptions are based "should not be considered a metric by which an accurate comparison of the vulnerability of one operating system versus another can be made." Yet I don't see an update on the WinInformant site acknowledging this, disputing it, or ANYthing.
If one actually READS the data, Windows came in at #1 for the year 2000, and Microsoft products grab 14 of the top 15 vulnerabilities for 1999.