My theory on this full tapered peg goes something like this, Jay.

When I have used a full sized peg that only has a short taper on the leading point, it has a high risk of blowing out the relish on the back of the peg hole. So I have adopted this longer tapered peg and am very happy with 20 years of use. All my pegs are hand made. Usually red oak. So, in the PE studies do they caculate the relish and the blow out that will happen if the peg is crammed into a drawn hole? Sure they do. You happened to leave out this factor in you strength calculations, it is not just the peg but the relish behind the peg and if that is compromised, the peg is of no use what so ever. By the time the joint is fully drawn and the peg comes to rest the cross section is withing specs of the hole. Also keep in mind there are many joints that are pegged that don't even need pegs, they are only used to wedge the joint together for assembly purposes.