The LED bulb might only raise the temperature inside the fixture a few degrees, but that could still be enough to significantly affect the cooling. Doing some quick calculations, an increase of only 4ºC in the surrounding air can decrease the rate of heat transfer by 33%.
With LEDs, overheating issues are more likely to manifest themselves over time, resulting in decreased lumen output over the life of the LED. (I do not think LED lamps under 12 watts are even an issue in enclosed fixtures)
With CFLs, on the other hand, overheating has less to do with being in an enclosed space (though it is still a factor), and is more likely to result in catastrophic failure, possibly even fire. CLFs put out more heat than LED, and while they may be a little less vulnerable to mild overheating over time, the base is still made out of plastic that could potentially melt. It is a completely different mechanism of overheating.