My reply was in response to Trollbait's question about price, not cost. Of course additional components will cost more in parts, labor, and warranty coverage. I suspect it is on all 2012 Volts as it may be more costly to build two variants. Probably the only difference is whether Chevrolet is going to warranty that the Volt will perform to those standards depending on the state, much like the CARB warranty requirements on hybrid batteries.
I meant cost. Carb packages usually don't change the price with most cars. The only number change is the 150+ horsepower engine losing a point. That's what I suspect.