CCFL backlight does not respond fast enough to changes in overall scene to scene brightness, as result it is not very effective. It is used to get an overstated high contrast marketing specification. Some LED backlight TV's do sub-segment screen backlight modulation which is even more effective then a total screen LED backlight modulation in truely increasing contrast ratio.
By some, you mean the very expensive, and very uncommon, rear lit LED ones - CCFL backlit sets seem to respond perfectly well to changes in brightness, LED backlights don't seem to give any advantages to the picture at all. Certainly in the shop here, I couldn't tell you which was which, without consulting the specs.