Hunh.
That is fascinating about the way the detents are so close to the end notches. Clearly not optimum, and I can see why things could get nasty if the mounting screw loosens.

I think it's also interesting to note that Shimano has three different indexing methodologies (half column like 7400 6 speed, six tab like 6208, and detent ring, like the illustrated bar ends) and that some of them -9 speed is a good example- are even different between down tube shifters and bar end shifters. 9 speed down tube shifters use the 6 tab system, but the bar ends use the detent ring system.