GNU su and the wheel group

[Tristan Miller]

Greetings.

Apparently there are some versions of su which will refuse to run unless
the user is a member of the `wheel' group.  GNU su refuses to implement
this check, because, as per a note from Richard Stallman in the info page, 

> Under the usual `su' mechanism, once someone learns the root password who
> sympathizes with the ordinary users, he or she can tell the rest.  The
> "wheel group" feature would make this impossible, and thus cement the
> power of the rulers.

I don't really understand this argument, for the following reasons:

1) If someone has the root password, can't they just log in as root from a
regular terminal or via ssh?  Or is it typical for Un*x systems to be
configured such that the root account can be accessed only via su?

2) Even if su is the only way of logging in as root, why couldn't a
"sympathizer" simply add all users to the wheel group in addition to
telling others the root password?

Can someone explain to me how having a wheel group is supposedly more
restrictive?

Regards,
Tristan

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