Do you have data to back that claim up? I remember reading evidence to the contrary, namely that programmers working on the same problem -- even in different environments -- tend to produce roughly the same set of bugs.
The conclusion of that study was that parallel development mainly accomplishes a false sense of security, and most of the additional reliability in those projects came from other sound engineering techniques. But I have lost the reference, so I don't know how much credibility to lend my memory.
After some searchengineering I found Knight and Leveson (1986) “AN EXPERIMENTAL EVALUATION OF THE ASSUMPTION OF INDEPENDENCE IN MULTI-VERSION PROGRAMMING” which my memory tells me us the classic paper on common failure modes in reliability via N-version software which I was taught about in my undergrad degree http://sunnyday.mit.edu/papers.html#ft
The conclusion of that study was that parallel development mainly accomplishes a false sense of security, and most of the additional reliability in those projects came from other sound engineering techniques. But I have lost the reference, so I don't know how much credibility to lend my memory.