How does "Richard Cory" by Edwin Arlington Robinson deal with the old adage "appearances are deceptive"?

Robinson's "Richard Cory" is a sad and somewhat chilling poem. It does reflect that old adage, certainly, that appearances can be deceptive.
The poem shows the people of the town admiring and envying him his life.  He was,

... a gentleman from sole to crown,
Clean favored, and imperially slim (Robinson lines 3-4).

Richard Cory was also well-spoken, handsome, wealthy, and "admirably schooled in every grace" (line 10).  The people believed that he had everything, everything that made them "wish that we were in his place" (line 12).  The people of the town led ordinary lives, lives filled with all the difficulties that life can be filled with. They worked hard, suffered from insomnia, 

And went without the meat, and cursed the bread (lines 14).

It is only in the last two lines that we learn that Richard Cory, the man who had everything, went home and killed himself.  So we can see, as the narrator sees, appearances do not tell us everything about a person, a person who seems to have it all, but succumbs to some dreadful sadness or anger in spite of this.  Those whom we envy, for whatever reason we envy them, may present themselves to us as happy and successful while they are drowning in despair inside.  We know nothing about a person by taking note of appearances only.