Agreed, though with regs you can never say never; flues in voids being retrospectively introduced is a prime example.
My argument was that the over-zealous RGI, given changes in regs that none of us can predict, may assume that because he can't inspect all of the flue that there could be a joint hidden in an inaccessible place (despite the protestations of the customer). If, at that future date, the regs say that a flue that can't be inspected along its whole route is ID (rather than AR) then the customer is slightly shafted - he has to bash a hole in his boxed in section just to show that there's no fault with the flue and no joints.
It's the same argument that you've just used in another thread in the last 30 mins, ie 'for the sake of a tenner install the TRV to prevent any come-back'.