Troy, I was surprised about the rough construction of the original pieces of furniture. My guess is they were built sort of as proofs of concept. I'd guess if sheetrock screws had existed at the time, he'd have used them.
From what I've read and seen, FLW was a great architect but not such a great engineer. I've heard that in preparation for a visit by House Beautiful or some other magazine to his house at Taliesin, he decided the bedroom wasn't big enough. He and his students tore out a load bearing wall and put on an addition. Evidently it wasn't long before the addition was all but falling off the house. They did a major restoration there a few years ago and fixing that addition was a major project.