I have to point out that a servo motor is just a motor with positioning feedback, and a stepper with feedback is still technically a servo motor. But let's just call it that since everyone seems to anyways.
I thought one of the advantages of steppers was they did not spark and the only other motors that run off DC (technically it's a really grey area since any motor can run off DC if you have the right inverters and drivers, but you get the idea) and don't spark are brushless motors. So if you needed a non-sparking motor with absolute position control but the electronics for brushless motors did not exist, were not readily available or too expensive, wouldn't that make a stepper your only choice? For either system you'd probably need feedback and gearing for good results.
The only two other advantages I can think of for a stepper motor are that it's much more straightforward to make a stepper hold it's position and that it's simpler to build than a brushed DC motor. Other than that, I personally can't think of what you would use a stepper motor for where you couldn't use another motor so it may just come down to personal preference?
IN my mind a stepper filled in the role of a brushless motor when brushless motors did not exist (simple, sparkless, but driver electronics are more complex than a brushed DC driver).