That's because they're in different market segments. The NEC PA27 costs a couple hundred more than the U2711 and uses the exact same panel - it's more tuned for professional use and has much better processing.
I believe Eizo has a model that uses the same panel or a similar panel that costs even more tuned for colour accuracy and image processing with more options for calibration etc. And then there's build quality and features/accessories.
If you have Eizo or NEC money, you won't be looking at Dells in the first place.