This euphonic change was originally used in Kyoto, and still remains in Western Japanese dialects. This change doesn't occur in Kanto or Tohoku region, but since honorifics in Uptown Tokyo, which is the base of Standard Japanese, is strongly influenced by Kyoto/Kinki dialect, this u-euphonic change is used only when attached to ございます and 存じます (e.g. おいしゅう(=美味しく)ございます, うれしゅう(=うれしく)存じます).