You are correct that Nikon and Canon entered with early models that were not stellar, except for price. However, that was also when digital was just coming into play, and nobody was sure how that was going to work or not. With Leica, it seems to be quite a bit different. They are coming to the party quite late, so they should have learned a lot more lessons than they appear to have when they released the M8. And they did have some digital experience (not all good, but not all bad either) with the DMR before that, so "excuses" start to get whittled away even more.
Not saying that they should not have some slack given, but honestly, they seem to be quite slow to learn and doggedly stubborn about "old ways" that may not be quite as germane in today's markets and with the greater demands and offerings in those markets. Not saying the M8 is not a very interesting achievement, as it is. It just should not have been released with as many teething problems, nor with the expectations that it was truly at the same professional level as other DSLRs, or its film predecessors, because it is not. The glass is wonderful. The body is wonderfully nostalgic, but lacks the finished details in operation, testing and use that their mechanical bodies helped earn their reputation.
I enjoy my M8 and lenses very much. However, I have not been able to count on it as the professional tools that I can always count on to deliver for me, as my Canons do. I prefer the M8 image to the Canon images, but I do not prefer the problems and erratics it also still brings, and should not. We all know "the list", and much of it has been repeated here.
I agree with Marc that one should never use "sunk costs" in making future investment plans. That includes emotions and "blind spots". This PJ should have tested the M8 and spent a bit of time learning about the issues before committing to it as his main tool. He, like a lot of us, bought into a lot of promise and marketing and maybe some nostalgia, and a lot of that was not being delivered by the M8. Has that gotten better? Maybe, but I still do not see it for use beyond my casual and travel interests, or as an "in a pinch" back-up to shooting assignments. But that is me.... I remain a bit disappointed with the M8, but that gets washed over every now and then when it lets me capture things that would be very difficult to get with other cameras. Love/almost hate relationship at times ;-)