Yes a DI needs to be through, but it's nothing like a genuine heavy landing inspection. For one thing you didn't routinely derig... I also wonder if 'modern' glass gliders are more robust. What causes the damage to ours is not running over frozen rutted fields - if they are that bad we don't fly - but in the case of single seaters poorly handled arrivals. Despite some excellent hangers we have also had hangar rash mostly where some pilots are far too eager to push a glider in and push too fast. We have also had ground handling accidents that have damage gliders. So yes, we are taught where to look for a DI but it falls well short of a real heavy landing inspection.