I guess what I'm saying is that it would make more sense to me if OpenBSD and Linux were both on the list. As you also mentioned, flaws existing in programs is inevitable, so unless the defect rate, normalized for usage, is significantly higher in one case, it's not good evidence for the quality or security of one over another.
In OpenBSD's case, the defect rate's pretty low, even when normalized for usage. It's had, what, 2 significant security bugs (that actually compromised the security of the base installation) over the last 2 decades or so? Pretty damn good if I may say so myself.
I guess what I'm saying is that it would make more sense to me if OpenBSD and Linux were both on the list. As you also mentioned, flaws existing in programs is inevitable, so unless the defect rate, normalized for usage, is significantly higher in one case, it's not good evidence for the quality or security of one over another.