I'm with Sgt Floyd... they're just something special about cell animation. Like how in the old 80's cartoons you can tell if something is going to move, like a landslide or something because of the colour of it as opposed to the rest of the background. *giggles*
There's a marked difference between theatrical animation and made for TV animation. They have more time with the film, higher budget, etc. Plus, they only have to show it once to make a fortune. A TV show has to air anywhere from 13 to 65 episodes a year, less budget, and shorter deadlines.
And let me stress this about the film....
No matter what kind of animation they use, it does NOT automatically mean it will be a great script or plot. As I said before, you can have beautiful animation, but when you have a lame plot and script, it don't mean a thing.
Look at Bullwinkle. The animation was terrible (unless they used the Hollywood studio. I thought that had some good looking limited animation for the times), but the plots were so funny, the voice actors were so terrific, it just didn't matter.