I missed this one. Andrew Cunningham, Ars Technica:
There is one minor benefit to using iOS 7 on a non-Retina iPad if you often find yourself using iPhone apps on your tablet. Here’s the deal: in iOS 6, iPhone apps will run using the same 480×320 resolution that they’d use on a non-Retina iPhone like the 3GS. Even if scaled up into 2x mode, the apps would simply scale up their non-Retina assets, meaning that you’d be looking at a 480×320 image scaled up to 1024×768. […]
In iOS 7, the 1x non-Retina display mode is entirely gone, and iPhone-only apps run in 2x mode and use their 960×640 Retina assets exclusively. The obvious upshot is that iPhone-only apps will look better on the non-Retina iPads.