If I may jump in with my graphics and web design experience...
It probably limits you to JPEGs because they're better for "continuous tone" images, specifically photos. The compression algorithms are better suited to that type of image.
GIF format images are better for abstract graphics with large areas of flat color, like a logo or those images that were kicking around for the patch design. GIFs might also be blocked because of some licensing issues that cropped up a few years back, but I doubt it. IIRC that only affected companies that created software that saves images in that format (Adobe, et al).
The problem I have with that is that the next time we start posting images for a patch design or something that is perfectly suited to the GIF format, we might be forced into using the JPEG format, which is inferior/inappropriate for that type of graphic.
Hope that made sense.
