Which is it? 500 watts or 35 watts? This summary and title are completely ridiculous, I can think of plenty of other things that are using more power in my home than a cable box. Refrigerator, freezer, washer, dryer, hair blow dryer, desktop computer, television, central heating/air conditioning, range (if it's electric), power tools/garage, home theatre system, the list goes on and on.
The reason the "500 Watts!!!" is disingenuous, is because many cable boxes have a switched outlet that allow you to plug in a television set to the back of it. Back in the good ol' days, you could click on the cable box and the TV would turn on as well, if it was plugged into the back. That CRT might draw as much as 500 watts, so that's what it's rated for. With the advent of universal remotes, electronic controls in sets that forget the last power setting and the need for constant power to keep settings and "quick-on" for many sets, this is now an antiquated port that's just a hold over from the olden days of cable TV.
The STB might be the 2nd biggest energy user in many homes, but I wouldn't bet on *most* homes.