Part of the reason they are so often used is that they are easily designed and easily performant. If something is a simple circle, you can load a graphic (or design an effect/shader) and simply rotate it.

If it's more involved (like the suggestion a few posts up), you generally either have to do horrible crap like qt-components did and load each frame of the image in sequence based on a timer, or load an animated image, or something. Neither are really appealing options.

*edit* especially considering Qt 5.2 has the capability to run animations that are simplistic enough entirely on the render thread: http://doc-snapshot.qt-project.org/q...-animator.html