The years following WWII the West entered a 30-year period of rapid economic expansion (in French the Trente Glorieuses). The Greek Economic Miracle was part of a larger economic boom, not one occurring in isolation. I don't have any detailed knowledge on this subject to appropriately discuss the causes, but the Wiki link you posted links to an entry that discuses them. Edit: grammar

I'd assume they use modernization theory and its S-shaped growth curve over time. That, and we should remember that the United Stated pumped substantial aid into the country.