Okay. Let's say the price is the same. Right now Canon and Nikon are bringing out really new top-of-the-line cameras about every three years. I'm not counting the incremental changes in cameras like the D2Xs, etc. For the incremental stuff, Leica's plan probably makes some sense, except for the fact that you lose your camera for a painfully long time while they add the increments.
But Canon's and Nikon's really new cameras are based on significant breakthroughs in technlolgy. If Leica's going to come close to keeping up with the technology, they're going to have to change most of the guts of the M8 within about three years. That means a new sensor, new shutter, probably a new rangefinder, a new processor, and new firmware. Ignoring the fact that Leica hasn't even been able to make a firmware change good enough to solve the M8's WB problem, let's assume they can provide all those new goodies and put them in your old M8 box. What do you suppose the price is going to be for replacing essentially the whole camera except for the box? As I said, let's assume the price is the same as the price of a new camera, though it's an assumption that calls for a major suspension of disbelief. Now you have a box with three years' worth of dings and wear, but with new guts. I guess you could tell yourself that you still have your good old M8. But I doubt there are enough people out there dumb enough to buy that approach to keep Leica in business.
I've been around a long time and I'm not any happier than anyone else with the kind of throw-away civilization we've built ourselves. I loved having cameras I could use for decades. But being unhappy with the situation doesn't change it. The kind of technology we have at the moment calls for a lot of throwing away. Maybe somewhere down the line it'll settle down. At the moment, Leica's living in the past. If they can't change that mindset they're on a path to extinction.