Yes, decent tips do indeed have a plated surface. Even indecent ones do. However, it's quite easy, especially when dealing with inexperience and large component leads, to puncture the plating. At that point, you find out rapidly how soluble copper is in molten lead/tin alloy (hint: extremely )

I personally use .4mm solder for most things I normally work with. However, for heavier work, larger diameter solder can be very useful, since you don't have to feed it into the joint so fast. Pinball machines that I have seen use fairly chunky connections, and large components on the PCBs, and my feeling is that very fine solder would be irritating to use under those circumstances.

pca