A receiver does not "need" video inputs, and most stereo receivers do not have them, although some have added that feature in newer models. Most if not all surround sound receivers added video inputs because someone perceived a consumer interest in switching audio and video inputs simultaneously from a single unit. There is some logic in that, especially since most analog TVs did not have multiple inputs until the home theater concept began to emerge. But many, myself included, feel that the best video quality is maintained by connecting video straight to the display, which we can do easily now with digital TVs that have a slew of analog and digital inputs. But many of the latest surround receivers now include some form of video upconversion, upscaling, and even half decent video processing that makes the concept a lot more appealing. But those added features are designed to sell the product, not make audio sound better, although an argument can be made that HDMI carrying both HD audio and HD video on a single cable has the potential to make even that point moot.
