It’s a surprisingly long list, and #1 is really good images. How long do you think it will be before e-books catch up – 5 years?
Print quality normally cannot even handle the image degradation of the JPEG format. It is possible to make printing-quality 300 dpi JPEGs (as you can see in the bottom half below), but they are very rare. Most of the 72 dpi images are disasters with massive artifacts around all the contrast edges.