NetBSD ships w/ nvi in-base. I don't have any other *BSD systems available at the moment, but according to http://en.wikipedia.org/wiki/Nvi#Credits_and_distribution it's the default in at least the "big 3" BSD distros (Net, Free, and Open; I don't know about DragonFly).

There are more than just two of us nvi users, and we're in good company :)

edit: This suggests DragonFlyBSD is nvi too, which isn't really surprising: http://leaf.dragonflybsd.org/cgi/web-man?command=vi