The funny thing about all this is that Oda has stubbornly and repeatedly stated that One Piece is a manga for young boys.
Toy Story 3 is also for young boys, and it's fantastic, and well-liked by adults also. It must be that youth re-expieriencing again thing that takes years away from us and makes us feel like little boys going on an adventure into the unknown.
It's actually very easy to let go. Just for a few minutes every week, just let it fucking go. It actualy makes a lot of sense that adults want to feel "young" again, if only for a few minutes a week. I'm supposed to be a fucking, sucky adult, but I just want to feel that awesome sense of adventure, carelessness, everything goes, that only Oda seems to do justice these days. So yes, it is perfectly understandable.
Also, understand that Oda is keeping a quality level that's pretty fucking high after more than 600 chapters, and he is not showing any intentions of slowing down his rythm. It's only normal that people aknowledge this, even if this same people is aknowledging Bleach and Naruto. They can't differenciate the good from the bad, poor guys. But we can, right? … RIGHT?