We need to be careful about what we are talking about here to make sure that people know if their servos are good or not, so let me describe what is normal and what is not with our servos:
The servo motor is a stepper, and when unpowered, it has some very small variation in resistance as you rotate the shaft. This occurs about 800 times per revolution of the output shaft. If you rotate the output shaft of the servo by hand slowly, you should feel a very small amount of of "notchiness" which is almost like a bad bearing or fine sand in a geartrain. It's very fine, very repeatable, and it gets smoother as you rotate faster because the inertia of the system hides it.
What is not normal is if you move the servo quickly and feel very big notches that have a huge amount of variation, almost like the servo is fighting you now and then. This only happens when you move quickly. This is indicative of a failed component inside the servo. We specifically test for this on every servo before it ships and have never seen this fail in the field, but we know it to be technically possible.
I admittedly think of the "normal" notches as so smooth that I don't notice them, but it is true it's not as smooth as a DC motor, and I was over-assuming that the original poster was referring to the larger, problematic ones.