No clue what the system is in Greece. It very well could have something to do with education level (whether they went to conservatory or not), years of service, and what position they take in the Church. But this is all speculation.
Once upon a time, in the Greek Speaking world only the chanters of The Great Church (TME as abbreviated in Greek) had the specific ranks of ProtoCantor and Lampadarios; Otherwise you were just The Right Cantor or Left Cantor of your church. Each cantor would have a Domestikos (whether in TME or not), and there would be Canonarchs as well. Nowadays you have many men with titles like "Protocantor of Greece", or America, or this Metropolis or that Metropolis. This is probably where the system comes from in Greece - Protocantors and Lampadari of various Cathedrals, Metropolises, chanting schools, heads of Choirs, and of the Archdiocese (Lykourgos Angelopoulos is the Protos).