Some redundancy == resiliance
Suppose the only-central-hub is corrupt/masonic(same thing)/incompetent/lazy/ has poor standards and high turnover? To claim one and only one outfit is better (for values of better) need proper justification. Secondly in five year's time when psycho-security or whatever is the rage then will the one-central-empire be able to compete honestly with Fred's two clever buggers who are surfing!
Some level of challenge to supremacy is always required. The alternative is an extra-territorial challenge that can catch Drake or whoever, unawares. Whatever system is adopted must embody FREQUENT, INTRUSIVE and DEVIOUS audits. The year's later crap from PWC is a waste of money.