That might be a theory, but I think it's probably 
that it's just  more efficient (and after they 
make the equipment changeover cheaper) to do it 
on computers.  

Because I can still pick up cels online or at the 
RISD art store... not exactly expensive... and 
celuloid or acetate or whatever they're making 
isn't just used in cels.  I believe x-rays are 
printed on celuloid sheets for example.  

My guess is it's more likely that the production 
has gone down as a result of computerization and 
not the other way around.

But hey, who knows?  Maybe anime cels contain a 
precious mineral that the world is running out of 
so we should start stockpiling ^_~