People could post comparisons in this thread perhaps? Maybe a mod could change the title. Here's a comparison of the game "Aerox" (great game, btw). Obviously the first screenshot (non-retina) has been upscaled to the same size as the retina screenshot so they can be more easily compared.
And how about on the ipod, the images are going to be small, and the details probably wont be that noticeable
without retina with retina I agree that it's pretty misleading to show the full sized pictures like that. Still a noticeable difference though.
http://en.wikipedia.org/wiki/Iphone#Screen_and_input Of course it's going to be smaller, you're looking at it from a distance. In that case the difference in detail would be even less noticeable.
The best way to see tue difference is to go to an apple shop or a phone retailer and hold up your old gen next to the 4th gen and see for yourself.