You can only cram so much battery into such a small enclosure and you would need a more powerful GPU that uses more battery for the retina screen. To all those that are complaining about the iPad Mini not having a retina screen, would you be willing to sacrifice battery life and performance just to get a retina screen?
The problem is not really the GPU: it's the backlighting of the display.
Light bulbs, even LEDs, are generally very inefficient and waste a lot of energy.
The GPU problem can be fixed: both the A6X and A5X chips are manufactured on a 45 nm progress. Apple has already switched to 32 nm processes for their other chips (think A5, think A6). If they switch to an A5X/A6X chip build on a 32 nm-line next year, energy usage of a 32 nm A6X (with quad-core graphics) could be similar to a 32 nm A6 (without quad-core graphics).
So the real problem is the energy needed to light up the display (with LEDs). Current-generation Retina displays need about double the amount of LEDs compared to the non-Retina displays.
This problem can be solved by using IGZO technology: 50% les LED lights are needed and the LCD panel itself is more energy-efficient. This technology is relatively cheap and saves A LOT of energy, and it will be available as of Q4 2012 and it is expected to be even better available in Q1 2013.
This means next year they can launch an iPad mini that's got a Retina display
and an A6X chip without the need for much bigger batteries.
Also, the costs of high density displays will definitely come down after 12 months.
If they launched the iPad mini with Retina display today it would mean:
- A thicker device
- A heavier device
- A huge battery needed, takes a lot of time to charge
- Energy usage extremely high
- Double the amount of LEDs needed
- Using expensive Retina displays
- A5X chip, high power usage, worse graphics performance than iPad 2
If they are going to launch an iPad mini with Retina display (and A6X chip) next year, it would mean:
- A device that isn't thicker (maybe they can even make it thinner)
- A device that's not much heavier
- A similar battery is needed as they use today
- 50% less LEDs needed
- Retina display will be cheaper and more energy-efficient
- A6X chip, better performance, similar power usage
Releasing an iPad mini with Retina display today would be stupid (when viewed from a business-perspective). Releasing an iPad mini with Retina display and A6X next year would be much smarter: you get a Retina display without any compromises and as a company you save
a lot of costs.