Yeah I know what a PSU is but it just sounded dumb to point that out as if it was relevant. But as I said, there is more than the bump in RAM required to do that kind of resolution, it certainly makes for different development requirements, which means it needs more powerful processing.
In terms of cost, the biggest problem is yield. This is the percentage at which they can make displays without throwing them out due to faults. When making an LCD panel, it's kind of an all or nothing thing. A few dead pixels is the most they can accept, but it can be much worse very easily. The retina displays on the iPhone and iPod are not the cheapest to make at all, but because of their size (despite having more pixels) the yields are much higher because there is less to go wrong. When we talk about bringing that size up to 9 inches with WAY more pixels, the yield becomes much lower.
Just think about the reason Apple is using a different panel manufacturer for the iPod Touch. It is because of costs, and because of supply. It's already difficult enough to make the IPS retina displays, and getting them out in iPhones as quickly as possible puts a lot of strain on their supplier. Having a different manufacturer for the iPod Touch allows there to be no extra strain, and so it saves money.
There is no chance of a Retina Display in an iPad in 2011, maybe in 2012.
