Yes, the question is not merely one of penetration, nor of avoiding arcane usage, but rather whether the word is standard English. There's no easy way to define

Yes, the question is not merely one of penetration, nor of avoiding arcane usage, but rather whether the word is standard English. There's no easy way to define that, which is why NYT employs someone to decide for its writers. Three criteria important for Corbett are mentioned in his missive: "Except for special effect, we try to avoid colloquialisms, neologisms and jargon. And “tweet” — as a noun or a verb, referring to messages on Twitter — is all three." Each criterion seems reasonable to me. Lots of words start off life as neologisms or colloquialisms and become standard. Corbett is just saying that 'tweet' in non-ornithological contexts isn't there yet. I think the argument is indefectible (one of my favorite standard English words, though it's not in the spell-check dictionary).