The article doesn't take into account the worms and viruses that targetted the platforms. That is why Windows seems to be more 'secure' than Linux.
Personally, I think the reason Linux has more breaches is because there are more Government agencies moving to Linux. As such, they are more interesting/worthwhile targets for hackers. On the other hand, which sane person runs mission critical stuff on Windows?
If they were to include the number of worms/trojans/viruses, Windows would come out tops, followed by Linux, then Mac OS X. Either way, OS X still comes out tops
It's nice news for all BSD distros (including Mac OS X, of course), but OS X as a server OS also has the 'flaw' of just not being implemented on a large scale. The really interesting question would be: What percentage of _tried_ cracks were successful for which operating system. The study does not seem to include scale, just a number of recorded security breaches.