The Dell U2711 uses the same LG made panel as the 27" iMac.
The dell doesn't have LED backlighting because white LEDs are inferrior to wide spectrum CCFLs in terms of color. Thats why the apple display has 72% color gamut while the Dell with CCFL offers 102% despite using the exact same panel.
Only RGB LEDs would have a positive impact on color but they are costly and doesn't reduce power consumption all that much. RGB backlighting as far as I know is only offered by the really high end 30" NEC monitors which are priced out of this world.