Working as a RP and using Google as the IdP, it appears as though Google utterly ignores requests for attributes as "if_available." The article linked below seems to cofirm my experience. Google only responds when attributes are requested as "required," which is not supported by OpenID Client AX. As a result, Client AX becomes useless when working with Google.

http://lists.openid.net/pipermail/openid-general/2009-April/017687.html