Bertie,
I think AlBags is correct regarding manufacturing costs.
The oven part of the cooker has its own safety cut-off device. This is the f.f.d. -- flame failure device.
This is the device that will not allow full gas flow to the oven burner until the probe from the f.f.d. has been heated up by the small amount of gas coming through the bypass.
Some manufacturers also incorporate a safety device to the grill. This works on the same principle as the the hob lid. i.e. if the grill door is closed, it closes a valve on the gas supply to the grill.
Hope this helps.