Also, you may find that it is a requirement that the BBQ be FIXED to the house in order to have it connected to natural gas.
That's not true. I have a natural gas Rinnai BBQ on wheels. My brother has a different brand natural gas BBQ that is again not fixed. Mine was purchased directly from Rinnai (knew an employee).
The convenience factor is great with Natural Gas. No worries about gas bottles running out at the wrong time or being at the mercy of petrol stations who like to inflate the price of LPG (and the bottles) when it suits them.
Cheers,
Jamie