Complex Games has a post entitled Playing Games are playing Toys.
"Life Sims are often a Sandbox an open play system, where the object or ‘toy ‘is the game. Let’s say Sims is the toy but you create games through playing the ‘toy,’ you create goals through playing the game. There are clear goals in Sims you need to for fill your needs."
I tend to agree with that. As I posted here before, " maybe the biggest challenge in nongames design is giving the player the opportunity (and incentive) to create their own goals and see the original 'implicit goals' as the means to achieve them".