tr_status.php has a filtering option for minimum severity. "All" and "Not classified" have the same effect and are therefore redundant.
If "All" is specified, the min_severity parameter is not used on the API call. If a severity other than "All" is specified, that is used. With the min_severity being specified as "Return only triggers with severity greater or equal than the given severity." (https://www.zabbix.com/documentation/2.0/manual/appendix/api/trigger/get), results are the same for "Not classified" (>=0) and "All".
Offering "All" is redundant and potentially confusing. Having a "Minimum severity of All" also doesn't make sense when saying it out loud.