Doug Smith W9WI ) writes:
KDKA claims (and is able to back up that claim) that they were the
first COMMERCIAL broadcast stations.

Except that KDKA wasn't selling any commercials back in 1920. (there is
some evidence WJZ - now WABC - was the first station to sell airtime to
an outside advertiser, in 1926. Before then, the economic justification
for a broadcasting station was to advertise the licensee's own
products/services.)

But to promote the owner's business is still commercial.

That was the early model. All kinds of radio stations owned by some
other business went on the air, and it was seen as advertising for the
business.

It's only later that a standalone model came about, where radio stations
were owned by third parties and simply sold advertising space in order
to support the station (and thus the business).

Michael