In addition to the answer provided by Tim Westcott I can add some additional information. to answer my own questions:
The internalinternal difference is the microprocessor that controls the motor. This has some implications for its use.
What difference should this make in practice?
Can for example SG92R motors simply be treated as drop-in replacements for SG90 motors in the same sort of application?
A digital motor cannot simply be dropped in as a replacement for an analog motor; depending on the application, it may behave very differently.
An analog motor has a much greater apparent dead spot around its current position. One consequence of this is to provide an built-in dampening effect. A digital motor is much more sensitive to small movements away from its current position, and will correct much more rapidly.
If the mechanism it's controlling is itself undamped, this can lead to violent oscillation as the servo's own movements repeatedly overshoot and undershoot the correct position.
In a mechanism where the movements of two motors are at work and interact, the slightest movement can result in uncontrollable behaviour.
Should they be driven differently?
When I'm driving them (directly from the GPIO pins of a Raspberry Pi) should I treat them any differently - for example, if I have been using a 50Hz pulse to drive them, should I change this or any other parameters for a digital servo?
In my tests I didn't see any difference in when controlling a digital motor using 50Hz or faster pulses, so as far as I was able to ascertain, they can be driven by the same pulse regime as analog motors.
Are digital servos more or less easily damaged than analog servos?
( i.e. by excess load, electrical errors, etc)?
I haven't been able to discover either in testing or research any clear difference in their ability to withstand mistreatment.
Several of the analog motors I tested simply stopped working and none of the digital motors, but it's not possible to say why.