The main reasoning behind this is that an analysis of approach incidents/accidents over many years showed that in 75% of cases the Captain was flying the aircraft when these incidents/accidents occurred.
fireflybob... I'm certainly not going to dispute the figure you quote. All that I'll say is that, depending on the number of years involved, the possibility is that the figure might actually pre-date CRM. The days when the Captain was God incarnate and the F/O was the Captain's sexual advisor...
