A larger file to picture ratio.. B psd compatibility...although Adobe is kinda close to the chest about that.

current ratio of file sizes, (Picture to File..folder), is kinda big... most people don't use pictures that big on their computer.. hence formats like jpg. Photoshop format would be very useful, ad it would allow for "invisible watermark" identification of proprietary images. But, like I said... Adobe is pretty close to the chest with their formats.