I've got a situation where setPropertyActionListener works, but actionParam does not. What gives?

The following code works, with setPropertyActionListener, in that the setExpandStateId method gets invoked when I click the link. If I change to actionParam, the setExpandStateId method does not get invoked. Why is that?

<h:form id="runStateForm">
 <rich:dataTable id="deviceStatus" styleClass="inner-fieldset-group" var="projectDeviceStateSummary"
 value="#{projectManagerBean.projectDeviceStateSummaries}">
 <rich:column>
 <f:facet name="header"><h:outputText value="Step"/></f:facet>
 <a4j:region>
 <a4j:commandLink reRender="deviceStatus"
 action="#{projectManagerBean.testAction}"
 immediate="true">
 <f:setPropertyActionListener
 target="#{projectManagerBean.expandStateId}"
 value="#{projectDeviceStateSummary.stateId}"/>
 <h:outputText value="+#{projectDeviceStateSummary.stateId}" />
 </a4j:commandLink>
 </a4j:region>
 <h:outputText value="#{projectDeviceStateSummary.stateName}" />
 </rich:column>

 <rich:column>
 <f:facet name="header"><h:outputText value="Complete"/></f:facet>
 <h:outputText value="#{projectDeviceStateSummary.completeCount}" />
 </rich:column>
 </rich:dataTable>
</h:form>

If I move the Ajax related code outside of the dataTable, then actionParam does work. See that code below. Very mysterious.

<a4j:region>
 <h:form id="runStateFormx">
 <a4j:commandLink reRender="deviceStatus" action="#{projectManagerBean.testAction}">
 <a4j:actionparam value="2" assignTo="#{projectManagerBean.expandStateId}"/>
 <h:outputText value="+2" />
 </a4j:commandLink>
 </h:form>
</a4j:region>