It comes down to a policy choice that is made, and I guess that in Canada the starting point for the adoption of this model, as opposed to the traditional model or the B.C. model, was the Marshall commission report, which said there should be a director of public prosecutions—in that case, for Nova Scotia—and that there should be some accountability. But they saw the accountability only being in respect of these important cases. They didn't see an Attorney General having to be informed or become involved in the vast number of cases.
On February 11th, 2009. See this statement in context.