Googling turns up
this page:
If you use <html :form></html> in Struts, there is no way for you to specify the autocomplete attribute. You will need to extend the FormTag class to achieve this.
Also note that the AutoComplete="on/off" attribute is an IE only attribute. It is not part of the HTML spec. I would wager that this is why it is not included in the Struts html:form tag.