4.3 /etc/shells

[Ron Natalie <ron>]

One reason is that /etc/shells is used for other stuff as well.
For example FTP will not allow FTP logins for accounts with non-standard
shells.  Some sites have accounts like "finger" or "who" which run with
a shell, uucp logins almost always invoke "uucico", you don't want people
to come in by some other non-login means to these accounts and be able
to bust out of the rather limited shell that they were given.

-Ron