Some people just feel better using the best (even if the "best" does not make any significant difference).
Marketing is amazing and any of use could be tempted to buy a high cost equipment (Like golf clubs as has been accurately mentioned) to have an improvement in our skills, on some could be a frustration knowing that it just does not help, on others the difference can jump right away.
Flying helis would be a good point of comparison, you really can feel the difference with digital servos, but helis are more precise machines than almost all r/c planes.
Personally I just do not know if my trusty JR 8103 has the resolution required to transmit the precision steps that a digital servo can use to improve any surface, but I know that the capability of the digital servo itself can improve the centering of the surface (I like to use them on elevator and ailerons only just because of their centering capability).
Digital servos are the future of the servo technologies so sooner or later we will have to move to digitals, even if they just do not suit our needs.

Regards.

Alfred.