HDMI Cables are Required for HDTV
When a salesperson is listing enough acronyms to make your head spin, you may not realize that the expensive HDMI cable he's putting in your shopping cart is only one of several ways to receive HDTV broadcasts on your new HDTV. Though they both have "HD" in their name, don't buy that HDMI cable until you know for sure that you need it for your HDTV.
High-definition Multimedia Interface (HDMI) is a standard for sending digital audio/video signals between devices. Authors of the HDMI standard include several big names in home theater equipment, such as Panasonic, Sony and Toshiba. In 2008, more than 800 manufacturers had adopted the standard, and 229 million HDMI-enabled devices were shipped to market [source: HDMI.org]. This list includes HDTVs, Blu-ray players, personal computers, game consoles and digital video cameras.
As described in How HDMI Works, HDMI is just one of several methods you can use to connect your home-theater components. Some connections, like component video convert digital signals to analog to carry it across the cable to your TV. If you're happy with the quality from these cables, or if you have older devices that can only use these types of cables, you can still use them to view HDTV video on your HDTV set.
Unlike component video, though, HDMI and DVI can carry digital signals. DVI, or digital video interface, is an older all-digital standard most often used in computer monitors. By avoiding the analog conversion, HDMI and DVI can provide HDTV video in its highest quality. DVI and HDMI share the same protocol for transmitting those digital signals across the cable. While DVI only carries video, though, HDMI can carry both video and audio.
So, in short, choosing an HDMI cable for your HDTV is not a requirement, but it does give you a higher quality than some other connection technologies when you're viewing high-definition video.