I had noticed the difference previously and I sort of attributed it a necessity given the greater number of priests in the Roman Catholic Church in addition to the Anglicized names.
Bishops in the Orthodox Church drop their surname completely although they'll show up in print with brackets around them whenever there are multiple Bishops with the same first name (which are taken when they take their monastric vows).
I don't imagine they're given to the usage common today among Roman Catholics of using the nickname form of the first name, e.g., Fr. Tom?