@Imitorar:
No, changing Zoro to Zolo in the manga was 4Kids' fault too. Viz wouldn't have done it if 4Kids didn't.
I've repeated the following many times over, but the fanbase continues to grow, so here's a brief lesson in One Piece history for those who hadn't heard it before:
Viz wouldn't have changed Zoro to Zolo if 4Kids had actually trademarked the names of the characters of a show that they dubbing. Either 4Kids didn't move fast enough or somebody decided that it wasn't necessary to do so, but the fact remains that Shueisha managed to trademark the names Monkey D. Luffy, Roronoa Zolo, Nami The Navigator, and Usopp in what must have been a bid to claim some of whatever merchandising revenue 4Kids received from said characters. Had 4Kids done so, Viz would have cheerfully ignored Zolo in the same fashion that they ignored Chaser and Trace.
But, snce Shueisha is their parent company, Viz didn't have any choice one way or another which names they could use since not using those names would undermine Shueisha's claim to the trademark.
How do I know all this? A search of the U.S. Patent Office's online database reveals that the names of the above characters were trademarked by Shueisha around August 2003 (it's been a while since I looked this up, understand, but it was around then), but Zolo didn't crop up until the October issue. That's because the September issue went to press in August. In addition, an article appeared in an issue a few months prior to the actual name change that featured a write-up of the impending 4Kids dub that noted that Roronoa Zoro would probably be referred to as Zolo in the dub, but that article as well as the chapters in that issue prominently featured the name Zoro as did the following issue. They seemed intent on keeping Zoro as a Zoro at that point. But it so happened that Shueisha noticed that 4Kids wasn't on the ball and we wound up with Zolo as a result.
Ultimately, the blame for changing Zoro to Zolo on Shueisha's marketing department or 4Kids' company-wide cluelessness where One Piece was concerned, not with Viz.