Is Linux as good as I think it is?

Now don't get me wrong, I'm a committed Windows user. I like the way I can mess with it and almost think I know what I'm doing. But this site has got me confused. It seems official enough. It's a US site from the .gov.uk domain. It's got a sensible logo. But it says this:

This bulletin provides a year-end summary of software vulnerabilities that were identified between January 2005 and December 2005. The information is presented only as a index with links to the US-CERT Cyber Security Bulletin the information was published in. There were 5198 reported vulnerabilities: 812 Windows operating system vulnerabilities; 2328 Unix/Linux operating vulnerabilities; and 2058 Multiple operating system vulnerabilities.

[emphasis added]

So that count gives more vulnerabilities in Unix than Windows? How can that be right?

Maybe some fanboys will come along and tell me where I'm going wrong.