Isn't there also a third option for those who wan't the image "stretched"? If you dont select any anamorphic mode, the 16:9 image just gets streched to the 2.35:1 screen. I wouldn't use it, but it's an option.If you select the JVC's Anamorphic Mode D, then you will have 'normal' 16:9 content, not cropped or stretched, with the expected black pillar bars on the side.
If you select the JVC's Anamorphic Mode C, then it will treat it the same way it treats 2.35:1 content, cropping the top/bottom area equivalent to where the Letterbox bars would be, and have the width fill the full scope screen.
So it's up to you - some people want the full original content, uncropped, and so use Mode D.
Others want to fill their screen, and are ok with cropping off the top/bottom of the content. They use Mode C.
And if you have an external Video Processor, you might have other options, with stretch, crop, or some combination of these two.