Where does it say that?
http://www.openbsd.org/cgi-bin/man.cgi?query=ifconfig
Pedantry, but keep in mind that there isn't really "the" man page for this.
Ubuntu might want to deprecate ifconfig, but that doesn't mean everyone does.
You're right, and I use OpenBSD myself so I should have qualified it. The man page I quoted was CentOS in this case.
This is Linux specific advice for ifconfig, correct?
NOTE
This program is obsolete! For replacement check ip addr and ip link. For statistics use ip -s link.