ujmot said:
Maybe the rear bar in the AWD version help with correcting some of the inherent understeer in AWD OR omitted from the RWD to help keep the handling more neutral? Wild guess.
Hmm, possibly. Most cars have a certain amount of understeer dialed in for safety; if the AWD naturally understeers more than a RWD, then the rear bar could help alleviate some of this, as you said. If this is the case, adding the rear bar to the RWD may tune the handling even more toward neutral or to even slightly oversteer; a more desirable trait in sports cars to those that know their stuff.
I used to have a Honda Del Sol S (very nimble little car, esp. with the mods I had), which came with a front sway bar only. The Del Sol VTEC model, however, came with a thicker front and a rear bar, the overall effect of which was to maintain the same balance and tendency to understeer, yet allow for less body roll. What I did was retain my smaller front bar and add the rear bar from the VTEC; the result was more neutral handling and less tendency to understeer.
If this all makes sense, then adding the rear bar to my RWD FX could make for more aggressive handling characteristics. Yummy.