Griff,
For a start, I'm not having a dig at all air ambulances, as I have a great deal of respect for the excellent service they provide. Secondly, I may have misunderstood some of the things I've seen happen. But for what it's worth, my point is simply that I have seen occasions when an air ambulance has got stuck in, sometimes of their own accord, when it seemed obvious right from the start that a SAR helicopter would be better suited to the incident, and this led me to wonder what the motives were.
For instance, a woman fell on rocks on the coast 2 miles north of RAF Boulmer and broke her leg (this is about two years ago). The call went to the ambulance service, who asked for an air ambulance. Being the weekend, the nearest one was in Carlisle; the aircraft launched, got to the scene, couldn't land anywhere nearby, so landed some way away, tried to reach her and eventually realized they couldn't do anything for the casualty (terrain unsuitable for stretcher carry, not enough people to do it in any case). At this stage, the Boulmer Sea King was requested, and the SAR crew recovered the woman in short order. Given that the location was shown on the map as an area of low cliffs and tidal rocks, I was surprised that a distant air ambulance crew decided to have a go when they knew there was a SAR base only one minute's flying time away. As it was, the delay while they attended meant the casualty spent the best part of an hour unnecessarily stranded. Another point is that the SK crew were surprised on arrival to find an air ambulance parked not far from the incident, given that no call had been made to Boulmer as the air amb approached (not mandatory to do so, of course, but good airmanship would suggest calling a SAR base when operating so close) - a cynic would surmise that the air amb crew didn't want to let on that there was an incident on Boulmer's doorstep in case the beastly SAR crew dared to resolve the situation quickly and successfully, and deny the air amb the chance to deliver a casualty to hospital. There are other incidents similar to this which I could relate but won't!
And there are the incidents which DDW alluded to in his post where it's difficult to understand why a lengthy and sometimes risky stretcher carry (two hours, in one episode I saw!) is preferred to getting a SAR aircraft. And the occasions when air amb personnel try to bully control room staff into giving them more trade (I've been told this in person by the boss of an ambulance service control room) while discouraging them from asking for a SAR aircraft by telling them that they will be charged for using it - the control room staff in many cases don't know any better and fall for this tripe!
Like I say, maybe I have it all wrong, but from what I've seen there do seem to be occasions when casualty welfare is not the over-riding priority when an air amb attends an incident. At the same time, what better way is there for a charity to keep the funds flowing in than to have an impressive list of people delivered to hospital...