yep yep, they have to list it that way, the tax is indeed $2100.00 (which off hand is more than any other SRT8 which slide in at 1300)
Below is the formula that is used and depending on the result depends on what the tax is. You must score 22.5MPG or more to be exempt from the tax. The tax also excludes vehicles classified as light trucks or business use vehicles.
(1/(.495/city MPG + .351/highway MPG))+.15 = Result
And the tax chart..
at least 22.5 No tax
at least 21.5, but less than 22.5 $1000
at least 20.5, but less than 21.5 $1300
at least 19.5, but less than 20.5 $1700
at least 18.5, but less than 19.5 $2100
at least 17.5, but less than 18.5 $2600
at least 16.5, but less than 17.5 $3000
at least 15.5, but less than 16.5 $3700
at least 14.5, but less than 15.5 $4500
at least 13.5, but less than 14.5 $5400
at least 12.5, but less than 13.5 $6400
less than 12.5 $7700
Gah more off topic.. here is the PDF for 2006 listing what vehicles required a GG tax.
Link