So from what I gather, both the digital and analog versions use a potentiometer as a position sensor. The only real difference is that the analog servos have a 50Hz signal and the digital have a 300Hz signal which improves the servo response speed. Also, almost all servos made today are digital. The only way to know for sure is to open the servo and look at the amplifier board at the base of the servo, and see if it has a processor. It's going to be difficult for most people to discern between a processor and an ASIC chip which the analog servos have.
In the end, the digital servos are only slightly better than the analog... so that's why there isn't a big push to change over. What people really seem to want is a durable/reliable servo that weighs almost nothing and costs almost nothing.