OK. Using 2 other emails I found the difference between the short form sign up and the actual subscription.
The actual subscription allows one to see the archives and post from the web. The short form does not allow that, but you can post from your email.
The way it reads is a bit confusing:
Subscription / Unsubscription To subscribe or unsubscribe from this list, please log in first.
You can also subscribe without creating an account.
It is not clear that in the former case you can use the web interface and n the latter you cannot until/unless if you later go back and do that.
I would suggest using "To subscribe and be able to see the archives as well as post from there..".for #1 and To subscribe to receive and post via email only (not as convenient) for #2