Said in 28 May 2012 MMD:

>[ I believe most American piano makers copied the designs of others
>[ instead of risking innovation.  -- Robbie

Intriguing question and belief.  I could not determine the rationale
(or source of rationale) but a really quick look at some of the early
U.S. patents for pneumatic player pianos shows that key locks were
often assumed, as early as 1903 and throughout the 1920s.

Most of the patents were based on the actuation of the piano movement
(not involving the keys directly), but in the 1903/1906 era there were
a couple of patents that were innovative and actuated the back of the
key, resulting in animated keys by design.

Brian Shaw