The truth is most likely that Oda is doing research in order to maintain the high standard associated with One Piece. I've said this before in other threads here(Naruto I think), that mangaka must troll the internet reading theories, pedictions and opinions. I think that sometimes the weekly format doesn't allow for enough discussion on from the fanbase on particular topics, so they throw a break in and let the latest chapters marinate. This way, Oda, the editors and their underlings can comb the internet for related forums and fan sites to get the bigger picture about how the fanbase thinks the story will unfold. If they do this they can ensure the plot is less predictable and also avoid pitfalls. I think they may even find some fan predictions better or more interesting than what they originally had in store for us.
If you wrote a highly successful form of entertainment in a weekly format that was widely discussed on the internet, wouldn't you read the heated discussions between your fans? Wouldn't you use this information to make your story even better?