Sometimes it still amazes me to contemplate that this proverb was invented at some point, and some fellow named Korzybski invented it, and this happened as late as the 20th century.

It surprises less if you realize that other proverbs have conveyed the same idea—I think, more aptly: "Theory is gray, but the golden tree of life is green." --Johann Wolfgang von Goethe

The Goethe quote (substitute "reality" for "tree of life" to be more prosaic) brings out that the difference between the best theory and reality is reality's greater richness.

On the other hand, there are two distinct points conflated by the "map versus territory" standard offer: 1) the map leaves things out (by design) and 2) the map gets things wrong (by error).

Because of this conflation, "map versus territory" is one of the most abusable cliches around, perhaps second only to "the exception that proves the rule."