According to the link there are differences in the use of the switch chip:
Ether1 port on RB450G has a feature that allows it to be removed/added to the default switch group. By default ether1 port will be included in the switch group. This configuration can be changed with /interface ethernet switch set switch1 switch-all-ports=no
all-port-switch=yes/no -
"yes" means ether1 is part of switch and supports switch grouping, and all other advanced Atheros8316 features including extended statistics (/interface ethernet print stats).
"no" means ether1 is not part of switch, effectivly making it as stand alone ethernet port, this way increasing its troughtput to other ports in bridged, and routed mode, but removing the switching possibility on this port.