A good example of this is Ghost in the Shell.  
There are alot of tiny CG effects added to it 
after all the cels are done.  Anyone who has the 
DVD and has seen the "making of" should know 
what I mean.  They use it to add new things like 
lens flares and some blurring of areas to create 
more depth, etc.  I think interest in anime's 
would drop a lot if they started to do 100% CG 
animes.  One of the aspects I so enjoy about 
animes is the fact that it was all (or mostly) 
done by hand by someone sitting in front of a 
table with a piece of a paper and an 
imagination.  And that's being done 30 times a 
second (or however many frames per second animes 
are).  And I like the "cartoonish" look that 
animes have.  I do think with greater 
enhancements in CG art will make actors or even 
stuntmen obsolete (too risky to have someone 
jump from a building? just use CG and it can 
look like him).  Just look at the Final Fantasy 
movie.  One of the goals of that movie was to 
make it look very realistic, and there are parts 
in that movie where it looks amazingly real.

I think us (Americans) as a nation has lost a 
lot of interest in cels.  People are more intent 
on buying the latest and greatest techno-gadget 
then collecting something that basically, in 
order to preserve them, you can't do a thing 
with.  Even hanging cels to display them can be 
dangerous on them.  And I think that the U.S. 
population would rather buy stuff that they can 
show off to their friends then something that 
they basically can't show to anyone besides 
pictures.  But as animes are becoming more and 
more popular in the U.S., who knows if that will 
change.