Chindenathus said what I was going to. Basically---a properly installed LED will last forever. My PS2's red LED has been going for years on end.
But most cheap LED installations like in keychains and toys, have no resistor/circuitry----they'll work, but only 1/1000 as long as they should. That gives then tens, maybe hundreds of hours of operation, instead of the thousands or hundreds of thousands of hours they would if they had a proper resistor. Going resistor-less means you can do it cheaper, and in a smaller space. But it won't last long, and it especially doesn't like to be on for longer than a few seconds, as it'll REALLY burn out then with no resistor.