@tzukishiro I'm not quite sure you mean it as
"all the others had a plot" (a real plot, not just a setting and things more or less remaining the same thorough all the story)
or as
"this is just the 41st chapter, probably one tenth or less of what will be the final length, so there will be plenty of time for the plot to be lost in the cycle of 'facing a stronger enemy/getting stronger and defeating them' without any real advancement in the knowledge of what happened between Mao, the Byouki and all the others"
The only one I haven't read is Maison Ikkoku (only read a few chapters and watched an handful of episodes of the anime), maybe I'm missing the only one with a plot, but as
@sleepyknight pointed out, Takahashi's works are mostly a collection of episodes with a common setting... If someone came, in Urusei Yatsura, and magically turned Lum into the strongest martial artist high schooler, you would get the second half of Ranma½....
Even for Inuyasha, there is an underlying plot, but there are also a lot of side stories that little have to do with the quest to defeat Naraku...