IIRC from my reading, the Bauers were introduced when
the show changed locale to Selby Flats (this may have
been in 1947, when the show moved from NBC to CBS).
Springfield didn't become the show's locale until the '60s
at the earliest, as I think someone has mentioned. So it
was actually the Bauers moving from Selby Flats to Springfield,
not the other way around. In the show's first decade (1937-47),
the principal character was Rev. John Rutledge (I heard Reva
make a reference to him the other day), played by Arthur Peterson,
best known as the old Major on Soap. In 1947 he didn't want to
move from Chicago to L.A. and so his character was written out.
The network change, and the introduction of all-new characters,
is similar to what happened when Y&R went to an hour. One
family, the Fosters, was written out, while Victor Newman (among
others) was introduced at that time.
Nevertheless, the television version of GL has always originated
in New York...and that's since 1952.