In an Entertainment Weekly article
Joel talks about a new host, new mad scientist, and new voices for Crow and Servo. One of the biggest missteps of the old series was re-voicing Crow with Bill Corbett instead of just coming up with a new robot companion. They didn't re-cast Joel Robinson, T.V.'s Frank, or Dr. Forrester, they replaced them with new characters. I like Bill Corbett and love Crow, but even if Bill Corbett was as good as Trace Beaulieu at portraying Crow (I contend he wasn't, though he had worse circumstances in which to do it) he would still be different enough to warrant a different character.
I guess if they're doing a total reboot with no continuity to the previous show, re-voicing the established robots would be fine, but I still feel like they should be retired.