I agree. Well, I'd expect him being the lead planner as he was for Graces, but that begs the question why one such wouldn't be mentioned among the directors and scenario writers.
Another interesting info (which the staff listing likely won't shed much light on) was the mention in the video interview with Sakuraba that he worked on the soundtrack for 14 months (which I hope nobody interprets as him having worked on it non-stop in that time =P). He usually starts working only late into the development, so this made me think that Zestiria was originally planed for release a year earlier. So if there turns out to be not much of an overlap with the Xillia staff this may point to a 'next Tales' sooner than expected, and we may have two groups again, something I'd actually welcome.