I wonder if the new development and release system they have might have a play in this. In TS2 it used to be 2 EPs and 3 SPs every year. SPs had no additional gameplay to them. In TS4 they divide gameplay between EPs, GP, and SPs, and since they cannot release just gameplay objects, they always include additional objects without new gameplay like furniture and stuff. Maybe they could add more gameplay if they didn't spend so much money on decorative stuff to fill out the GPs and SPs.