The S.Zero did in fact come with the larger rear sway. Remember the S.Zero was Honda's product offering for those customers who wanted to buy a NSX-R, which was not in production at the time. In many ways, the S.Zero was a testing ground for features that would make it into the 2002 NSX-R. For example, it has the dual-disc mainshaft in the 6-speed transmission and the wet-clutch LSD- features carried over to the R. One feature that did not make it over was the rear sway. While it worked very well with the Type-S suspension, a lot of people did not like how it interfaced with the NA1 NSX-R suspension on the S.Zero. I recall a Best Motoring segment where Gan San said the car was too twitchy compared to the NA1 NSX-R.
The NA2 NSX-R reverted back to the small factory rear sway and many NSX racers remove the rear sway entirely from the car. We can only guess, but it is likely Honda added the bigger rear sway to help balance out some of the understeer they added by changing the dampers and springs in the Type-S. This would result in a more lively-feeling, "tossable" car at street speeds. For the S.Zero, which was intended as a track day car, it might have made the car too loose at track speeds. This was an issue for the original NSX too and is why Honda did what it did on the NA1 R. It seems they corrected the S.Zero balance problem on the NA2 NSX-R.
