there is absolutely no difference 
between someone putting the colour down with a 
brush, or with them clicking the dump-colour 
button. 

Just my 2cents... as a traditional illustrator 
AND a CG artist.

I disagree.  I have also done work in CG, and 
compared to the fan cels I've painted, CG is much 
easier. For me, painting cels is harder than 
painting on regular media, partially because 
getting the texture of the paint smooth but thick 
enough can be very hard, and because the lines 
are so unforgiving.  If you screw up, you can't 
just paint over the top (okay, granted, 
correction layers- but I tend to make a lot of 
mistakes).  Mixing paint tends to be a nightmare 
because any variation of the color shows up - 
again, perhaps for a pro this is easier as the 
colors are premixed.  In addition, hand inked 
lines are a total bear, in my opinion, and I 
think it takes a lot of artistic talent to make 
them look even and perfect (perhaps tracing is 
simply not my strong suit).  
But I would say CG is much easier, mainly because 
mistakes are so much easier to fix.