"Oh, and the benefit from making the anamorphic is a higher quality... I know, this has been denied by many people, but you should consider that any possible compression artifacts get squeezed together (or only stretched horizontally, as opposed to a zoomed letterboxed image), and become teeny-tiny... well, at least less visible."
Expanding to anamorphic makes any visual glitches larger along with the rest of the picture, and they are still going to be compressed in the image - thus being especially visible on the widescreen image that they are intended to be shown on.