You just said yourself, that you need to create a higher resolution assets for a retina display app. And then you have to recompile an app, test it, upload to the app store... a complete cycle, right?
That's correct, if you don't already have higher resolution assets you can simply resize to the appropriate resolution, then you'll have to create them, and then you (should) test the app (to make sure you've not made any typos and all the appropriate @3x images are being used) and upload when you're done.
On the other hand, supporting an entirely different resolution would require that you test your layout and make changes to your code to support it. Which could take a substantial amount of time if the app has many hard coded lines in it, or just if the app is quite large.
In addition certain content needs to be optimized by developer as well for the retina display. For instance, an original fixed layout Kindle book running in the Kindle App for iPad 2 would occupy only a quarter of the iPad 3 screen. So again, ebook developer has to to through a trouble of rebuilding the book, testing it on at least 4 devices and resubmitting to Apple. It's too much work. OS has to be smarter than that.
That's not true, iOS automatically handles rendering everything at the higher resolution. When you're designing any app (OpenGL ES apps/games aside) it's designed for 480x320 or 1024x768 points, which iOS then translates into pixels. The eBook developer doesn't have to rebuild the book at all.
When going to 1440x960 the internal resolution (or actual workspace) remains at 480x320 points, and iOS translates that into the higher resolution. Games aside, all apps are compatible with this and games need only have their target resolution set to the new resolution.
All in all, the only thing developers need to do is provide higher resolution assets. There's not really any testing needed, and it's a lot less work and simpler work, than supporting another layout.
IPS is still a backlit LCD with its all shortcomings. It is dated technology on the way out.
- I would like on the next iPhones to see some flavor of OLED display.
- I would like to see a resolution-independent iOS
- And I would like to see Apple offering iPhones in different sizes, e.g. 3.5", 4.5", 5.5" to meet various consumer needs.
I would like to see the next iPhone using an IGZO display, and 3.5 and 4.5 inch displays would be good.