sure, the statistics are going to be inaccurate in the great debate of which is the best os (m$ vs linux)
taking into consideration that the source is freely available for linux and you also need to take into account that because m$ has been so much more widely used, it is naturally going to be the most targeted.
i think that the recent change in the vulnerability ratio between the two oses is due largely to the indication that linux is gaining in popularity with the masses.