N'kay, O'Tink...this is what I learned about temperamental artist FLW...if you (the owner) agreed to keep his creation fully in line with his artistic intent, he would give the owners a signed plaque you could post in the house!
...and, he had a habit of dropping in without notice to MAKE SURE you were not violating the artistic integrity thereof. So once he dropped into this house Cedar Rock, and the owners had displayed a set of canisters in the kitchen that FLW did not like; kerfuffle! Finally FLW agreed to let the canisters stay in the house but the wife had to keep them closed inside the pantry!
So yes, my guess would be that the furniture was immovable so as to ensure artistic lines... but do go see this house if you are ever in Quasqueton, IA...it DOES seem to have a way of making people fall in love with it...I certainly did...
...and I think I recall this house is the ONLY one in Iowa that has his signed plaque, FLW and the owners had become good friends in the process of building Cedar Rock, 1948-1950, I think it was...