I'm pretty sure that Sheldon wrote that incorrectly and if you read it you'll see that it seems to contradict itself.
The 9-speed shifters work with 8-speed Dura Ace with no changes but they won't work with 8-speed Ultegra rear derailleurs.
If you look at Sheldon's "Index Interchangeability Chart" it shows that.
Sheldon does on rare occasion make mistakes as I demonstrated one time with French components.