A loyal customer base with deep pockets apparently. It may be better, but To me it seems a lot like the rampant rapeage that goes on in the audio industry. It may be the difference between 5% better than a Nikon priced $4000 cheaper, but that hardly justifies the price difference AND there's probably something out there thats just as good for much cheaper.
I doubt it's 5% better. It's more a different look to the photos. It's hard to say a Nikon or Canon setup couldn't do as well. The big advantage the M9 has is size. It just makes street photography so much easier and it's less offensive to the subject than the larger outfits.
But try taking sports photos with a M9. It can be done, but it's not ideal. So I see a camera like the M9 as a tool for a certain style of photography. Like I said, I'd love to have a Leica kit but I'm not in the economic demographic. My whole Canon kit wouldn't get me a M9 and a 28 ASPH lens.