Yeah, but if you use a 256 color palette overall, you can save just as much space by having certain sprites and so forth use fewer colors. Of course it's unlikely that with a 256 color palette the artist is going to actually use all 256 at any given time. With the low resolution of the SNES, and given a medium-small sized sprite, for example, you can't really make much use out of more than 2-3 shades of each color you're using in the sprite. 16 colors is generally more than enough for your average sprite, and combining a bunch of those with a 128-color background layer, your raw space usage is going to be about the same as it would be if you had used the same 16 colors for all the sprites. Of course compression is a factor, but I don't think serious compression was used on many SNES games anyway... although SFA2 uses some pretty heavy compression, I would imagine.
