After seeing the iPad mini, and reading the reviews, I still wonder why Apple didn’t go for retina in their device.
And after thinking about it for a while, I think I’ve got it figured out why.

The iPad mini currently has a resolution of 1024x768 at 163dpi. This means the apps written for the iPad can run unmodified at a slighty smaller size on the iPad mini.
Coincidentally, the display panel of an iPad mini has the same dpi as a nonretina iPhone.
Coincidence, or clever planning by Apple.

Now, let’s say Apple wanted to go retina with the iPad mini.

Scenario 1

The easiest way would be doubling the resolution of the released model, to make it a true retina screen. This means using a 2048x1536 resolution at 326dpi. Sounds familiar? Well, it should be because that display is the same display as a retina iPhone.

In theory this works, the same apps work in both the iPad mini and iPad in retina resolution, only the touch targets on the mini are still a bit smaller as the full-size iPad.

The downside: the iPad mini with a 326dpi display have a far better retina quality than the iPad at 264dpi. Selling the retina iPad as retina wouldn’t really be justifiable I think.
And this display is more expensive, making the 329€ target price more difficult to reach.

Scenario 2

They could also do what they did when going from the iPhone 4 to the iPhone 5 and keep the same display panel, but just cut it in a different size.
Take the display of an iPad retina, and cut it down from 9.7 to 7.9 inches: at 264DPI this gives us a 1678x1250 screen.

This makes developing apps a lot more complicated: developers need to design apps for a new screensize, apps now not only need to contain an iPhone and iPad payload in both retina and nonretina size, but would also be designed for a 7.9 screen specifically.

Comparing these three options:

  • iPhone 3Gs screen (current solution)
  • iPhone 4 screen (better quality than iPad retina, more expensive)
  • iPad Retina screen cut down to 7.9 inch (custom app builds)

I think it’s logical Apple has chosen for the first solution at this moment.

In the future I see Apple upgrading the display to a retina iPhone screen once prices go down.

Update 6/nov/12
I did this thought exercise with DPI and resolution in mind.
Various people mentioned I forgot to include power consumption and weight.  But since I don't have any facts about how much more power a retina screen uses I've decided not to include this aspect.