Microsoft gives Internet Explorer a perfect score (4 points!) for security, and they say Chrome only deserves 2.5 points. I'm not sure it's worth doing a full debunk of this. It's the same "Look, we have more checkboxes filled in" type of marketing that was more common in the boxed software era. The checkboxes are pretty arbitrary or omit important points, e.g. MSFT says that Chrome doesn't block insecure content on HTTPS, but Chrome users have had that option since June: http://googleonlinesecurity.blogspot.com/2011/06/trying-to-end-mixed-scripting.html
If I were designing a benchmark, I'd probably choose something like "the odds that a typical user of browser X will be infected by malware" and try to minimize those odds. My guess is that's what the Chrome team tries to do.