Further clarification: LED-lit rear-projection DLP TVs (what I have)—using one red, one green, and one blue LED—have been out for awhile and are pretty cheap.
The benefit compared to other rear projections TVs being that they don't have a bulb to burn out. The downside of course to a rear-projection being that they're quite thick, and the viewing angle is poor.
The LCD LED TVs are newer, use white LEDs (I believe), are just as thin as previous LCDs if not thinner, and have the benefit of the backlight not burning out. When a fluorescent backlight burns out on an LED, you're out of luck, they're generally not a replaceable part.