usually has to do with the lense of the camera, and the lense not being able to focus all of the different wavelengths (colors) of light at the exact same focal plane. And basically some pixels on the plate become "over charged" and affects the pixels around it
you can sort of repair this on photoshop n stuff, but getting a better lense would help also
Yes, the chromatic abbreation. It seems to be a problem in digital camera, even in those "pro-sumer" type camera... I guess they put more work in the electronic rather than the optics...