I don't think the characters of frequencies, or something you said are the important differencies between a stepping and a servo motor.
I think the most important difference between the two types of motors is that their physical characters which are:
1) The stepping has hold torque, so that, as you drive a stepping, you can hold it at a right position, while as you turn off a servo, you will make free running.
2) As their structures, a stepping will be much bigger than a servo.
3) You can use PWM to both types of motors
4) You can use H brigde to both
5) Servo is driven in a close loop controller, while they usually use stepping in an open loop with an external motor model.
6) Servo motor is run continuously, while stepping run with its steps. You may use good stepping with 0.72 deg per step, and drive it under half step mode, it provides 0.36 deg per step. And as you run it in microstep, you may get better results about 1/8 step, that is 0.09 deg per step. It seems to be continuous.
7) There many types of stepping motors such as unipolar, bipolar, multiphase or permanent magnetic motors, hybrid motors, and variable reluctance motors... but they are all DC motors. But servo is only one type of control, and they have DC servo and AC servo.
8) You may use a stepping to work as a servo motor if you add an to it an encoder. You may use higher level driver such as L297 with H brigde L298 to drive stepping as easy as a DC motors. Important to note that servo is a one type of control theory, and they use it with DC motor, you will have DC servo motors, they use it with AC motors, you have AC servo motors.
Goodluck