Thanks @Cheese and @rvieceli for the links. May have to pick on of those up.
As Ron noted, on the one-piece step drill, the pilot has a very limited amount of drilling depth (because it is a pilot). The proper way to use this item is to drill the pilot hole to the depth needed and then use the step drill to give the desired amount of counterbore depth while using the original pilot hole diameter to center and guide the step drill. It will always be a 2-step process.
With the carbide counterbores, you have more options for the pilot diameter as well as the pilot diameter drilling depth. Select the counterbore diameter, select the pilot drill diameter then assemble them to attain the pilot drill depth desired and drill. It is a 1-step process.
It just depends upon the product/manufacturing requirements.