Why does the OP and ED of most animes use different art styles than the show?

Question

I've noticed recently that most animes from 2002 to recent use different art styles during their OP and ED when compared to the main story. From a non-artistic standpoint I can understand that since the same OP or ED is used for a large number of episodes that they can put more details into them and other aspects without having to spend a lot of time on it. It's done once and used from then on. I also understand that some use Retro styles just because they can and it makes you laugh. This question is for the in between styles. They look similar, but it is obvious that it was done 'Differently'.

BUT the difference is sometimes so drastic that you can't even tell they belong together. Characters end up with such different looks that it takes you a moment to comprehend what is going on. While I do not find it a bad thing I feel that the work and detail put into the ED and OP could have also been placed into the story and made a world of difference.

My most current example: Chocotto Sister and its ED. It is a 2006 show, but the ED animation would have put it in the 2010 or 2011 category in my mind. It has that much of a difference.

(This question refers to OP and EDs with movement, not static images.) (Be aware, Chocotto Sister has topless scenes. Please be wary if reviewing an episode. NSFW)

Answer 1

I can't speak for every anime in the 00s, but the storyboard artist for the OP and the ED for Chocotto specifically are different, according to ANN: http://www.animenewsnetwork.com/encyclopedia/anime.php?id=6674 - So that may have influenced the end result.

And oftentimes you'll have studios working together, sometimes one influencing the entire episode of a series or its opening and ending. ( Shaft does this a lot and Mad House has done some work with Ghibli: http://en.wikipedia.org/wiki/Madhouse_(company)#Collaborations )

Answer 2

Opening and Ending animation sequences are supposed to attract viewers and so the producers put more money into their making than in the same time length of the main anime.

Usually it's a minute and a half of lots of visual effects and alluring action packed together with cool music and you see that every episode. Imagine how quickly you'd be bored if it was animated in the same simpler technique as the main part. Or how much less would be the probability of you staying for the main part if you saw such OP or ED.

It has to take more human resources than drawing main part of the anime, so it's often done by more people and they may be different from those who do the main animation. So it's natural the visual style is different.