Of course there are a lot more people in S Wales than N Wales, which might just mean that there is more demand for air ambulance flights in S Wales. I have seen gross misuse of charitably funded air ambulances by some Ambulance Service Management, so I am very suspicious of simple measures such as the one quoted in the original post. It does no harm to have a critical method of selecting suitable jobs for air ambulances.
I love the way that in life while one part of a group are trying to separate out a perfectly sensible joint use of resources(e.g. Emergency Service Helicopters in N Wales), another bit of essentially the same community are busily being forced to work together (Emergency Services Control Rooms to be combined) against their will.
........ And then in 5 years time someone will have a bright idea to save money in N Wales by combining the air ambulance and police helicopters into one aircraft to make best use of expensive resources.....
Aren't politicians wonderful!