That said, the thing that really nails it for me, and I suspect many others (putting aside development reasons), is the integrated experience. I love the fact that my iPad, iPhone, and Mac work with each other, etc... And once you're in that type of environment, and you have money invested in Apps, etc.. its incredibly difficult to want to move away especially when the experience is great (we can argue the semantics of what constitute as great but lets keep it simple and say good enough for most people).
The move from Windows to Mac was not a difficult one (at least for me). There was no integrated environment and as far as software, new software releases come out all the time so an upgrade or new purchase was going to happen sooner or later. I suspect that a lot of adopters that will be adopting Windows 8 will most likely be existing Window users. They will still dominate the shares in volume but I suspect new Apps on Windows at this point will be a challenge getting Mac users to switch off.