Short answer: story.
Longish answer: As people have already reiterated, Pixar doesn’t just make movies for now, they make movies that will have the same impact in 10, 20, 50 years time, as when they first premiered.
One thing I noticed in watching Ratatouille, is that it was a really funny movie the first couple of times I watched it. When I watched it for the third time I was a bit worried that I wouldn’t find it funny, therefore I wouldn’t enjoy the movie. I was pleasantly surprised to find out that even though the humour wasn’t new, and didn’t have the same impact, underneath the humour was a very touching story with layers of meaning, metaphors and message that had a big impact on my life and way of thinking.
I love how you can watch Pixar’s films and find something new and take something away from them every time. Or watch your favourite Pixar film until you can’t take watching it even one more time, then months or even years later, you go back and can see the film a different way, from a different point of view and see something that was always there to begin with, but you had never looked it that way before.
It’s this type of layering that I believe is absent from any of Dreamworks’ films. I don’t believe they have the same ideals as Pixar because Pixar believes that making films (using CGI in the case) is a form of art - a way to portray their message. They use the medium to its full advantage, but don’t let it take the focus off the story.
Dreamworks on the other hand, thinks that delivering the story using CGI is good enough to keep the viewer entertained. It isn’t. It’s only been roughly 10 years since Pixar’s first feature film, but already people have clued onto the fact that Pixar are the frontrunners between the two companies, because their films haven’t aged one bit, and Dreamworks’ already have.
Imagine what it would be like watching Shrek 3 in 50 years time! People won’t understand it because the story is set in the now - it won’t pass the test of time. Kind of reflects Dreamworks’ way of thinking, doesn’t it? Only thinking about the now, and what money they can get from passing off these mediocre stories as entertainment, just for a quick buck.
What Pixar is doing isn’t just delivering quality films for this generation and many to come, they are establishing themselves as another Disney. With Pixar as as it is now, well imagine if in 50 years time it could be like what Disney was during the golden age of animation (and hopefully what Disney will be like once again). Pixar could be just like Disney.
Another postive aspect that will outweigh any financial loss of Pixar’s (in the short term), is because Pixar is building a name you can trust. In the future the question “What is the difference between Dreamworks and Pixar?” will be not worth asking, because the answer will be clear and all because Pixar had the sense all along, from the very beginning, that the focus needs to be on the story.