Happily, I'm not into douga/genga. ^_-

And I agree, it does seem WRONG to sell douga 
separate from the cel THAT IT CAME WITH. I look at 
it like buying a pack of [something] with each 
item labelled "not labelled for individual 
retail sale." 

HOWEVER - 
And this gets tricky - for some collectors it is 
understandably impossible to buy the original cel. 
And, in most cases (unless it's a digital anime), 
the douga will always sell cheaper. While this may 
leave an ethical bad taste in many people's 
mouths, it also provides a reasonable avenue of 
collecting for some people who are huge fans of 
Eva or Kenshin but with limited pocketbooks, for 
instance. ?? I'm ambivalent. -_- *sigh*