Smajdalf:
Arduino alone cannot drive 45 other chips - the combined capacitance of wires and inputs is too high. CrossRoads had Arduino driving a few HC125s and each HC125 was driving a few 595s.
Yes, I understand an Arduino can't drive that number of outputs which is why he used the serial to parallel shift registers. I wanted to know the requirements that led to the use of the gate buffer IC.