Where lies the difference of this:
<h:inputText id="it" value="#{login}" required="true" > <a4j:support ajaxSingle="true" event="onblur" reRender="it" bypassUpdates="true"/> </h:inputText>
<h:inputText id="it" value="#{login}" required="true" > <rich:ajaxValidator event="onblur"/> </h:inputText>
<h:inputText id="it" value="#{login}" required="true" > <rich:ajaxValidator event="onblur" reRender="it"/> </h:inputText>
No. rich:ajaxValidators handles JSR-303: http://jcp.org/en/jsr/detail?id=303 validation annotations, that is its main purpose.