Hrm- then there's also Raff's overture with the same theme, and
the same title, but written in 1864.  According to information at
http://www.raff.org/ this was written to celebrate the 25th anniversary of
the accession of the Duke of Nassau, which duchy (among other places) used
the familiar tune as an anthem; Raff's home in Wiesbaden was in Nassau (no,
not the Nassau county of Long Island, nor the Nassau nickname of a certain
Ivy League college...  ;)

I wonder why Weber would use God Save the King in .his. overture, unless
it was also the anthem of the municipality whose ruler he was feting?  If
so, it might have gone by a different name than God Save the Queen .or.
King, just as Raff's did (I forget what name it went by in Nassau
offhand.)

Just a suggested alternative explanation.
-Eric Schissel
http://www.lightlink.com/schissel ICQ#7279016