I have heard that the Japanese love the film 
because it reminds them of a simpler time of their
childhood.  And it has very beautiful scenery and 
backgrounds with the trees and green fields. 
It stuck an emotional cord with them.  Also it is 
so darn cute, has an innocense (spelling?)
to it that you do not find in many films. 

Believe that when it first was shown in the 
theater that it was paired with the film 
Grave of the Fireflies, a very strange double 
bill. 

w.b.