It's not because Japanese people are cleaner in public toilets - I have seen enough "dirty" toilets in Japan to convince me that it's not the key factor. The secret is simply very frequent cleaning - in some toilets you'll see a list with stamps showing when the cleaning lady came during the day, and it can be as frequent as every hour.

I'm all for it. Having no free public toilets is just another reason not to go out or to feel annoyed staying out for too long. In Japan since this is free people can shop for longer and spend more time in public places and I am pretty sure this kind of factor has a positive effect on consumption, which is why malls and areas with large concentration of shops usually have the cleanest toilets.