Maybe add the above link which expands on what you've said in the gas-fitting FAQ.
Also when it says "A flexible hose connection should be used..." that begs the question "why?". I can think of a few reasons:
To allow the hob to be readily removed from a fitted worktop for servicing, To allow for simple fitting of a new worktop without requiring gas certified kitchen fitters. To enable completion of 1st fix as far as the bayonet outlet, before the kitchen fitters arrive. Plus, I suppose, it must be a nightmare soldering in a fixed supply upside down under the worktop. And possibly to permit the householder to swap out the hob for a new one at minimal cost.
Phil