[has2k1]

I mentioned the difference

"a structured/formulaic way to think about and build graphs"

This is what plotting using the "grammar" provides. Each plot is a like a sentence, for a sentence can be composed using some of the following - verb, noun, adverb, adjective, interjection, pronoun, proposition, conjunction. Alike, ggplot2 allows you to think of a graph in terms of layers, which layers can have different components that describe the "geometry" or "statistics" of the plot. Plus, there is a lot more.

You could probably describe your favourite plotting package as structured and formulaic, but an experience with ggplot2 would convince you otherwise.