Most Cable TV customers are perfectly content to use the "freebie" DTA (Digital Terminal Adapter) that the Cable company gave them, and run an NTSC analog signal on channel 3 or 4 in to the back of their set, and listen to mono audio.
Others do the same with their SDTV box....but, at least they get EPG and can order PPV.
Others purchase "HD Cable", but watch it via the RF output, or via composite (video, left, right) cables.....not component or HDMI.
Same with satellite. They get an HDTV, and they buy SDTV service, with an SD box.
Or, they get an HD box, and hook it up wrong (as above).
Many buy HDTV service on the main satellites, but don't have the separate dish required for their locals in HD, so they watch their local stations in SDTV, and claim their stations are "too cheap to broadcast HD", or "can't make HD look good".