I'd just like to add a wrinkle here that messes up what people see at home. The big cable stations like FX, TBS and TNT are offered in SD and HD versions on my cable dial (Verizon FiOS).
When they show an "old-style, 20th century" (as Spock would say) program, it looks fine, with black pillars along the sides, on the SD channel that nobody watches. But simultaneously on the HD channel that everybody watches, they stretch the image horizontally to fill the wide screen.
Ohh, you're kidding. That's horrible. I can't understand how anyone can tolerate watching TV that way. Yet apparently a lot of people don't even notice the distortion or don't care.