One consideration is that apart from everyone on here, a lot of people have no clue!
If they order a car through a cheap finance deal, they will have the car as it comes. I would assume most people buy 19"s for the looks and may not bother with the additional cost of Dcc, especially if it adds to the monthly payments and takes it out of the special deals that will inevitably be on offer, once orders for those that must have the new and shiny have faded.