It really doesn't matter if you specify flaps in degrees (0, 5, 10, 15, 30, 45) of flaps by numbers (1, 2, 3, 4) at some point they had to be verified as meeting a specific degree at each point (plus or minus a specific amount).
However, IMO using using flaps 1, 2, 3, 4 is just another example of removing the pilot from have and input into flying the airplane. ie they don't need to know the exact flap position just a number?