I've heard this arguement that Japanese are somehow culturally disinclined to sequels or continuing sequels, but this really takes a simplistic view of their popular culture.
Just because their television shows tend to be self contained ( a set number of episodes, encompasing one story arc) does not mean there are not episodic, or continuing stories.
There are several high profile series/movies that have spawned on sequels or continuing seasons that featured the same cast of characters in continuing adventures. Also, there are several well known series that just keep going on and on, year after year, building on story arc after arc, featuring the same characters.
Personally, I find the notion that somehow Japanese people are so abstract in their thinking to betray more of a romantacized and simplistic view of Japanese culture than anything else.