The biggest killer of LED's, is heat build up. Most fittings are designed for tungsten or halogen lamps, where heat does not really matter to the lamp, so long as the fitting can cope with it. Most fittings are well able to cope with the tiny amount of waste heat from LED's, except the LED's themselves cannot cope with high temperatures, the tiny amount of heat they themselves generate. They need good ventilation, better than most fittings are designed for.
A fitting where the LED is none replaceable, will have been designed from the ground up, for an LED.