anime like to spoil the story by over explaining the plot (fillers, I am looking at you Naruto) and how they like to go over broad the fight scenes for three to five episodes (DBZ). As for One Piece I enjoy the story, but as soon as the voices changed from the 4kids dub (I liked this dub), I just was not feeling the new Luffy and the others. Is funimation going to re dub the whole series or just continue from were 4kids left off (they should b/c it just sounds weird when the voices change, this is not an Ranma 1/2 series).
As for your ? about why the shows are not popular in the US, if it is not an Shonen Jump Series (I think that most of the shows that are made are from this company), it doesn't really do all that great unless their is a large fan following (Subs), it was cheap to buy or word of mouth. I mean every time I go to Borders or any place that sells Manga at big US chain, all I see is either an Viz title or Tokyo Pop, I know not everyone goes to comic book stores or the internet in the US to buy Manga, so if you see a title that is continued to be stored in bulk at a store, you will wonder if it is good and might buy it, which is why we got your Bleach, Naruto, One Piece, Death Note, anything Dragon Ball (all these are Viz manga titles ), etc. being shown and dub in the us because it is the availiblity of the Manga in the US that made these shows well liked in the US.
but because like Shaman King and One Piece, 4Kids edited the shows so badly (minimum violence, etc.) that the anime was not liked which lead to the shows not being well liked. any ways if every one had their way their would be a thread for every anime made because everyone likes different things, which is why it is good to being up an topic like this to discuss about why people like this anime, or the mangas, but yeah One Piece is a good read.