Except that regulators don't like liquid CO2 at all. I know an anti-siphon tube sorts out most liquid problems, but still you often see expansion chambers fitted before the regulator, with the two parts forming the foregrip.
Of course though, liquid is not a problem with nitro, so you don't want an expansion chamber. Assuming the tank has a regulator fitted already (usually the case if you're buy in a screw-in replacement for CO2), a secondary regulator isn't necessary unless you're running at low pressure.