They started making it 8 years ago (they had many 
production/money problems), that is at a time 
when there was no real alternative to cels - at 
least in Japan.

And last but not least, I just read that Otomo is 
going to come to Paris for the release of the 
movie. There will even be an exposition about the 
movie in an art gallery - and they said there 
would be a few cels...