Piano timbre is approximately harmonic. The inharmonicity is subtle enough that you can ignore it and it will still sound okay. Same is true with plucked string instruments. You're still using Western music theory.
I'm just struck by the zenlike simplicity of the original question, "What is a Major Chord?", compared to the random bits of technical jibber-jabber that would confuse the hell out of a poor soul who would dare to ask such a question, both in the linked blog post, and the discussion here.
I picked one of them for the title of my post, but I'm trying to answer them all.