What is the difference between hdr and non hdr photos on the Iphone 4?

Is it just higher quality when it is on hdr or is there more to it?

High Dynamic Range.
There could be a huge difference if you are a camera (and games in some cases) lover.

just visit this site and see the difference between them
http://www.geeksugar.com/What-iPhone-4S-HDR-Setting-22847963

HDR stands for "high dynamic range"-the range between the lightest and darkest areas of the image-and the idea is that they look more similar to what your eyeball sees than regular photographs.

… Made of several photos…

HDR images are achieved by blending several photos with different exposures-usually at least over-exposed and one under-exposed-to make for a more dynamic scene.

HDR basically takes 3 shots & combines them into 1 to make a perfect exposure shot.

1 in high contrast
1 in low contrast
1 neutral.

Here's an example.
image
non HDR shot

image
same with HDR