Nope. It is good that Theo is so paranoid^Wpassionate, but it isn't a whole reason. The whole reason is that so many people are involved, both on contributing and seeking design or coding flaws. Crowd-sourcing is the key.
I didn't say that opening the code makes it secure by a magic, what I said is that if the code is useful for some skilled people they will fix and improve the code, at least for themselves. Good ones will submit the patches back to the community.
So, fuck off.