Dear Mr. Venkatnarayanan,
The quotation by John Williams from Brahms's Academic Festival Overture is quite appropriate. Brahms wrote his piece as a thank-you for the an honorary Doctor's Degree in music given to him by the University of Breslau.
In his piece, he quoted from several well-known tunes that were sung by college students in those days. So John Williams is paying homage to the proud history of collegiate life by quoting Brahms here.
In a similar humorous vein, in Saint Saens's Carnival of the Animals, in the movement called 'Fossils', he quotes from children's songs that were considered to be out-of-date, and therefore 'fossils'.