Ya, it really is this simple for buff/debuff designations. The API has gone through so many revamps to streamline code changes in the past couple of years. You should take a look if that sort of thing interests you.
As for the green fire, I remember the response very accurately:
"Each green animation would be a whole new spell as far as the game is concerned." The way the spells are animated would also require a good investment of art resources; not just a simple tweak on the color slider as some believe.
Not exactly sure what the technical hindrance is to the backpack, other than sorting out how everyone's items fall into it, but I think someone recently said -quite aptly- that the larger backpack doesn't solve the space limitation issue. It just delays it. Investing resources in a [bag-free] tabard-sorting system and figuring out which items can be bag-free currency is probably more efficient.