Hi DaveW and Denis Y,
I cannot speak on the current Genesis and Summit range, but the Genesis 1000-5500 range, and the Summit Silver/Gold/Platinums DO have different valves on the main burners between Propane and NG. The difference is due to the amount of gas that is required for the burners to run on the lower settings.
Running the burners flat out seems to work OK, but if you use the wrong valve type the main burners can flame out on the lower settings.
That is not good as the gas keeps flowing.
The side burners and roti burners seem to work fine just by changing the orifaces, but NOT the main burners.
LMichaels was the first to advise me of the different valves, and I was very skeptical. But he was absolutely correct.
And yes, you should have a NG regulator for your NG gasser.