The Waltz in Der Rosenkavalier

Did you ever wonder exactly why Richard Strauss uses the waltz throughout his comic opera Der Rosenkavalier?  Considering that the story takes place in mid-18th century Vienna (a time when the waltz had not quite developed yet) it seems a bit anachronistic.  And yet, Strauss makes it work so well!  Listen to a theory proposed by the great conductor Georg Solti and a few choice examples from the score!