Point. I've had to use ed as well, but generally speaking, in all but the most dire of circumstances, vi will run -- I think on Solaris that vi is still statically linked. Even so, ed works very simmilarly to vi (including movement, search, save, and so on), so it's a lot easier to fix something with ed if you're a vi user. :)

seconded, there's no vi in openbsd install image

i had to use ed during installation to change the fstab (from sd0a to wd0a) of a 2.5" hdd mounted on usb

important step coz o/w rebooting from sd0a 2.5" ide put me to single user w/ read-only fs (too late for ed)