How was your vacation?
Although I agree with your assessement of how Japanese companies work, my view is that Canon is not just a Japanese company, it is a World company that has clearly understood that marketing is best handled in each geography, the North American market being most important for them. Let's face it, although they sell great products, their overwhelming success in the US has also a lot to do with smart marketing.
Besides, very much because I also know Japanese companies very well, having worked daily with them for 8 years now, I know from first hand experience that leaks that are not supposed to occur very rarely occur.
For what it is worth, the French magazine CDI made it clear on their web site last week that they also think that the leak was once more orchastrated by Canon. They find it very frustrating, since they are forced to stick to an ambargo while they feel Canon releases themselves the information on their side through leakes. Don't you find it to be a problem?
Their arguments: Canon does it because people like rumours, and the interest generated by leaks on internet forums is larger than what a plain press release does. Besides, the actual identity of many of those forum posters leaving very positive comments on the camera is un-known (are they real?) but the net outcome is most often a positive momentum for the camera before any magazine has the chance to release an objective/critical review of the specs. How convenient isn't it? This can also be a double edges sword though, and Canon did screw up a little this time with their poor landscape sample.
The leaks do also create a feeling of intimacy with the brand, especially when the rumours are confirmed, very much the same feeling used by movie makers who are good at telling people stories whose ending they already know.
What is the actual impact on sales? Very difficult to evaluate I guess, but why not do it if they feel that it can help? This is probably in the end just their instantiation of some "internet age marketing best practise" sold by some US marketing think tank, and I am sure that those guys produces convincing figures.