Bill,
I don't think you're lying, but you are mistaken.
composed an html web page containing my plaintext passwords and sent
it to me. Not decrypted by my browser after combining it with a
locally stored key. "
So, you're not describing all of the possible ways to decrypt data. What's happening is that the keys to decrypt the passwords are handed to your client (with some checks like a local admin password or pin) when you attempt to decrypt a given password. The passwords _are_ decrypted on your device and you did not get a HTML page with your passwords. Please, go look at the source yourself. What you got was a page that's almost entirely javascript and that includes the functions that handle the decryption.
Don't take my word for it, "
When you log in to a website while signed in to Chrome, Chrome encrypts your username and password with a secret key known only to your device. Then it sends an obscured copy of your data to Google. Because the encryption happens before Google’s servers get the information, nobody, including Google, learns your username or password."
If you want the technical details, please take a look at this paper. It goes into detail about the process for Chrome, Firefox, and LastPass.