I think what "Up" succeeded was even more significant than that: they took animation into the affective territory of live-action movies. Frankly, I don't even really remember the voices.
Making cartoons (which I sincerely believe 3D has been) has been one-upmanship of technology that pretty much builds its own history in lockstep, but to combine that with writing and the animation choices for something that can bring a tear to the eye of an adult is truly great work. The first act of "Up" really is a landmark to me.
Up also made excellent use of 3D to add to the emotional feeling; the way they handled "depth" in the sad introduction was different to the way they did it in the fun scenese or action scenes.
Making cartoons (which I sincerely believe 3D has been) has been one-upmanship of technology that pretty much builds its own history in lockstep, but to combine that with writing and the animation choices for something that can bring a tear to the eye of an adult is truly great work. The first act of "Up" really is a landmark to me.