Maybe you missed that memo, but it IS the typical usage, as I've observed it and confirmed with others. You don't have to believe me, but I've gotten a surprising number of upvotes (here and elsewhere) as a result of posting about this topic, so I think I'm not being crazy here.
2. This actually follows trivially from #1, in that ANY thought crime (looking at porn, coveting, thinking disrespectful thoughts of an elder, etc.) is de facto NOT about a relationship, and therefore can't be "unethical."
You may not believe #1, and if not, well, your loss. Not interested in arguing about it further. But you shouldn't be confused as to how #1 can imply #2.
There's additional confusion from the fact that "Ethics" as a topic of study is often just a synonym for "Morality," (capital letters) which doesn't take into account the colloquial meanings of "ethical" (lowercase 'e') and "moral".
tl;dr: English actually sucks.
I am fine with "Ethics != Morals".
However your explanations seem suspect:
1. I disagree entirely with the comments "ethical/unethical pretty much always refers to a relationship" and "ethics are about relationships"
2. "Some things that are clearly immoral in one value system or another are clearly NOT unethical in any system of ethics." -- This confuses me. Can you give me an example of an act that is CLEARLY IMMORAL in one value system and also CLEARLY NOT UNETHICAL in ANY SYSTEM OF ETHICS