Its amusing that I can recall similar debates when the first Range Rovers came out in the early 1970s. For years, a lot of Series enthusiasts insisted that the RR could never be as good off-road as their "real" Land Rovers. It was too comfortable, too fast, too quiet, too sophisticated. It had flimsy coils instead of big beefy leaf springs. It wasn't helped by the fact that very few owners wanted to risk taking their shiny new Range Rovers on tough off-road trails and expeditions.
There are still lots of advantages to Series Land Rovers over the newer coil-sprung, permanent 4WD Land Rovers, but no-one now would deny that they were (are) both great vehicles.
I don't know how the LR3 will pan out in the long run, but I have seen them being driven over some very difficult terrain, and perform superbly - much to my initial surprise. I wouldn't go so far as to say they are better off-road than a Defender 90 (they only have traction-control in their favour, but they have a worse power-to-mass ratio, worse grounding angles, less wheel articulation, and bigger dimensions to deal with). I would probably bet on a stock LR3 against my stock Defender 130, though, given similar tyres and equally experienced and willing drivers.
However, the point of the thread is not about the LR3's prowess (or lack of) off the road, but whether there is a design flaw or major QC problem with the control arm. I think it's a useful idea to publish details of incidents like this on the various forums, so we can get an idea of common defects. But I think the slightly hysterical reaction to what appears, so far, to be a rare occurence, is actually counter-productive. At this stage, if I drove a Discovery 3, I'd take a look at the state of it underneath, but I wouldn't lose any sleep over it. My attitude would change if this started to be a common occurence.