Yes, you can theoretically use the largest resolution image and have the UIImageView scale the image down using mode Aspect Fit.
The only drawback is the older phones that don't support retina also are less performant. For example, when using images on cells of a UITableView and scrolling, the device has to load the large image, then scale the image down, and scroll it at the same time, and it will stutter on old, slower devices.
So, perhaps just use multiple images in list views (should just be thumbnails and are tiny anyway, or just use the smaller images here), but don't worry about larger images that stay on the screen and don't scroll.
Make sure you load images in list views using methods that allow caching like imageNamed:.
As long as you take into consideration the performance penalties involved in scaling down the images, you can use just the largest image and scale it down to fit.
By the way, yes I've used this technique in real live apps in the App Store.
Another technique I've seen is to include lower quality images (1x or 2x) and if you run it on a higher resolution device (2x or 3x), automatically download high resolution images from the web. Maybe be nice about it and only download them on wifi.
Thank you for answering, I am supporting the only non retina devices I am supporting form iOS 7 upward is the iPad 2 and iPad mini 1. And I am loading the images as you suggest with imageNamed: Thank you for confirming that the technique works.
Also, Apple upped the maximum app size that you can download over cellular. It's now 100MB (was 50MB).
Much easier just to upload the highest res image and be done with the 2x and 3x business. If you use minimum size 2208x2208, it should cover all devices. Run your images through some compression software and you'll reduce size. Here's some info: paintcodeapp.com/news/ultimate-guide-to-iphone-resolutions