These are necessary for Concours participants. Otherwise we prefer the Phillips head screws which are easier to use without slipping and bunging the screw-head.
Sometimes Porsche cracks us up by the extent of their frugality. There were many parts that were used for many years, such as these, used for 12 years. Phillips head screws had become popular in 1936 but Porsche was probably able to get the old style screws at much lower cost.