Hi,

   First, I'd like to say I'm not attacking anyone
^_^...just pointing out something.  I don't think
the original poster was attacking, but he/she was
also pointing out...exactly what you
said...OPINION...  it is the other person's
OPINION that sketches should never be separated
from cels...  There is a difference between
opinion and fact.

   I think (and other's may disagree -- after all,
I'm only stating my opinion) that sketches and
cels can stand alone as individual works of art. 
I like my cels to have sketches, but for me, it
isn't a requirement.  If a seller would sell cel
*ONLY* if they could keep the sketch, I don't mind
them keeping the sketch...And I've purchases
sketches too.