> Actually, that's not quite true.  
> Specifying TLSv1 or SSLv3 on the
> server side will disable SSLv2.

There are use cases like FTPS where it is desirable that servers support
SSLv3 *and* TLSv1.
To do that by using OpenSSL SSLv23 protocol must be specified and SSLv2
must be explicitly disabled afterward.
As far as I've understood, using SSLv23 on the server sides means that
when the client connects it could decide whether using SSLv2, SSLv3 or
TLSv1.