Are iOS applications required to have retina images? All my research indicates that the answer is "yes" but I'd like some external confirmation from a source I trust (either Apple.com or this site) as I have a bunch of non-retina images and would really prefer not to create retina graphics.
No. You could submit an app with purely hand drawn images or 8 bit old school graphics and soundtrack

The only required retina assets are the store icons and app icons as specified in the iOS HIG:


https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html#//apple_ref/doc/uid/TP40006556-CH27-SW1