The fact that postscript(and by implication pdf) encodes circles via bezier curves is an implementation detail, "arc" is a primitive of the language, there is n

The fact that postscript(and by implication pdf) encodes circles via bezier curves is an implementation detail, "arc" is a primitive of the language, there is no reason your PS to g-code interpreter would not use circles for arcs. On that note, circles are rare on machine tools as well, if it is not a lathe(or rotary table) it will have to approximate a circle via a set of linear movements. Nothing wrong with this, modern machine tools can generate very good circles, often better than the rotary table, due to the additional error introduced by having another axis.