There are two reasons. In every department that I know of, there has been a wide delegation, almost absolute delegation, from the minister to an official or more than one official in the department. This official has the power to apply exemptions, grant extensions, exclude material. In other words, they have full power to do whatever they think is necessary. The act is crystal clear. There has been jurisprudence galore to interpret it.
On March 30th, 2009. See this statement in context.