Indeed, they could benefit aside from the fact that GIF has a 256 color pallet restriction...
Perhaps the (abet, lesser known) MNG (Multiple-image Network Graphics) is a better alternative? It is basically an animated PNG file, and is under the same licenses, etc (GAE supports PNG).
GIMP can export to MNG, which works the same way as it exports to GIF. It could be quite fun to see such a feature included, since as John said, imagine something like a water element that ripples and shimmers... Plus, some things could be easier to animate with an image than with a model (or even impossible to model sometimes). Of course, for those features, MNG would be MUCH better alternative to GIF since GIF only supports 256 colors and one alpha channel, which would make team color difficult, as well as limit quality poorly.
More info:
http://en.wikipedia.org/wiki/Multiple-image_Network_Graphics
