Actually the NW system also did it automatically, just not always as quickly as people wanted. As I recall, the updates were done once a week, on Saturdays. If your next flight after gaining a new status level was in the same week you needed to call in to have your WP number removed and reentered.

I went from gold to platinum on the outbound NW flight of a ten day trip to Paris. By the time I returned to the US my reservation showed the new status, without my doing anything about it. The AF lounge even allowed me access!