> Somewhere, either in a forum such as this or on the web, I came under
> the impression that Listserv works by putting all subscribers' email
> addrs in the bcc field.
>
> Can someone give me a technical explanation of whether or not this is
> true?

It's technically not correct, although the net effect is similar.
LISTSERV puts the recipients directly into SMTP RCPT TO commands
that specify where a particular copy of a message is to be delivered.
It does not generate a bcc field.