Powertrain for warranty purposes refers to internally lubricated parts. The clutch is a wear item and only covered by the basic initial warranty.
Any cases you may have seen reported where clutch repairs were covered beyond the official warranty period would be individual "goodwill" decisions by the particular dealer and/or SOA. If you've been a regular customer at a dealer for service you might be able to work something out with them, but if you come in off the street with your hand out looking for an out-of-warranty repair don't expect it to happen.