No, I didn't misread your post.
The OP's original post and the title of this thread is "Do you need US passport to exit St.Thomas".
You specifically stated "U.S. citizens do not need to carry any papers identifying them as citizens.", which is an untrue statement.
To enter or exit the USVI, you need a passport, drivers license, or birth certificate. Upon exiting the USVI, keeping the title of this thread in perspective, if asked for your proof of US citizenship, you must provide one of the three aforementioned documents. You may disagree with me, but you are not going to get very far (jail?) arguing with Homeland Security, it's the law.
Read about the Real ID Act:
http://www.dhs.gov/real-id-public-faqs
The same goes for Customs, you must show proof of US citizenship, which can be a passport, drivers license, or birth certificate, all in accordance with the law: the Real ID ACT.
This thread has nothing to do with being asked to show your ID while standing on a street corner in Wyoming. You can not treat reentering the US from another country, including USVI and Puerto Rico, as if your standing on that US street corner: you are not. Even after your plane lands, you haven't officially re-entered the country (US), until after you've cleared customs, meaning you have to show proof of citizenship: your still not on your favorite street corner yet.
So, to state "U.S. citizens do not need to carry any papers identifying them as citizens.", is wrong.