To most cel producers, cels are considered to be
useless after they take the picture of them.  So,
stapling them wouldn't really make any difference
to them.  Also, it is a very convenient way to
keep them organized and no one can see the staples
in the camera.  

What I do with all of my cels is just remove the
staples.  I don't think it will devalue them at
all.  As a matter-of-fact, it will probably halp
preserve them if you removed the staples since
metal tends to oxidize (rust) after a while and it
can discolor the cel.

Star Phoenix