Japanese dont litter ? This must be a good joke !! Japanese litter everywhere where they feel safe to do it. Go to a Hanabi Taikai (fireworks in summer) and on your way back you will be WALKING on litter for 1 kilometer. Go hiking in the mountains and you will see the extent of Japanese littering when noone is looking. Mountains of cans thrown away by hikers. Go in the countryside and see whay people leave on the side of the street. Oh yeah, they do litter just like everyone else, they are just a little more ashamed to do it public, and in the city the public services are just very efficient at cleaning up anyway.
After reading tourist books about how Japanese people think it's rude to blow your nose in public... it is slightly disconcerting to visit and see a guy hawk up some phlegm and spit it on the street. And/or, you step on a frozen goober, sparkling in the sun.
Even to the extent the generalization about a culture is true, there will always be interesting exceptions.
