I can tell you why it is a game pack. Because - it took more hours to make. And devs hours mean more money --> higher cost.
So for the game to properly rate your work (redecorating job) it has to know how. So they had to make a system for it. I am not sure what they chose but probably - they had to add to every single object in the game extra value. Like for example - color. So sims can recognize it. And probably it has to be per swatch not only the object. Unfortunately this system means - IMHO - that we will never have a color wheel.