I don't know whether Apple is out of the 16:10 display (30") market or whether the technology/supply wasn't there (spring/summer of 2010). Their 27" 2560x1440 display offers nearly the same resolution (minus 160 pixels of vertical real estate). Dell's rather recent release of the U3011 widescreen IPS display (which also uses an LG panel) indicates that Apple could now release a 30" display. Whether or not they do it is another story.
Dell's 30" is $400-500 more expensive than the 27" variation, although Apple could get back into the market since they focus on the high-end (thus the reason why they don't have a 20-24" model).
Based on the Dell spec. page, the 30" consumes about the same amount of "typical" power and both have a power consumption of 2W in sleep mode. The dimensions are roughly 2"x3"x0.5" bigger (HxWxD) and the 30" weighs about 3 pounds more.
Now, Apple might not see a market for this, but I figure there are quite a number of people willing to purchase a ~$2,500-2,700 high-end iMac with a 30" display. It would also provide some more room for cooling, although not by much.
However, I would put the chance of Apple re-entering the 30" display market at slim, instead offering 16:9 displays for the iMac and Cinema Display.