It's illegal in with cars to have dark tint.
That's why some manufacturers like Subaru classify their Outback and Forester as a truck - Subaru doesn't need to raise their CAFEconomy, but does so to be able to tint the rear windows.
In the case of the HHR and PT Cruiser, it has the dual benefit.
Unless a vehicle has flat folding rear seats and can be classified as a truck, it cannot have dark privacy tinted glass in the rear windows from the factory. At least in the US.