LCD comes in a variety of flavors...
Flavor 1: Flat panel display
Unlike your PC display, this display includes a very large backlight that is designed to very evenly distribute light across the entire display. It also includes a large power supply internally so that you only have a single plug from the display, to your wall to connect. Finally, it includes all the necessary connectivity and processing on board to connect from multiple formats to your home A/V system. It's not just a 'big' computer LCD. It is far more. What secifically, of what I listed, kicks it out the extra few inches? I'm not sure really - I haven't pulled one apart.
The other LCD technology is rear projection which runs at about a foot or so deep. This actually uses a projector inside of it projected though a very small (1" range) set of 3 LCD panels. Unlike an LCD flat panel which uses a very large LCD matrix right at the surface, these 3 small LCD panels are buried down inside the projector, then lenses, and mirrors direct the image up onto the rear projection screen.
DLP power consumption isn't that much. It is a rear projection technology, like LCD rear projection. The actual MMD (mirror chip) inside the projector has individual mirrors that flutter side to side hundreds of times a second to produce the various colors and different shades of those colors. I forget what the exact number is, but there are hundreds of flutters possible, every second, by each one of those mirrors.
The main power draw in these technologies is the projection lamps which are often 200 watts or so in current draw. The hz reference is in terms of image refresh rate, not so much tied into the current draw. Not an electrical reference.