As near as I can tell from reading the PSE Installation Instructions, the additional LED on the Sport button indicates that the PSE is ON. (I still think this is redundant. Maybe it is a legal requirement of some sort.)

I think the DME senses the pressing of the Sport button to ON (Sport mode) and turns ON the PSE through the connection from DME to PSE Electic Change-Over Valve. On NON-Sport Chrono cars the additional ON/OFF button replaces this function of the SPORT button on cars WITH Sport Chrono & Sport button. At least that is how I have deduced the operation.

If anyone has a clearer understanding of the operation of the PSE system in Sport Chrono and NON-Sport Chrono cars, I would like to hear what they have to say about the operation of the PSE.