Even though it will be up to the players to create alot of their own content, I imagine their is still alot of things that will be put into the game by Maxis. All the graspers and such that were parts Will put onto his creature, while everything could be manipulated, if you want to have lots of creative options, their will have to be lots of base parts to be manipulated. Also all the things like spears and the campfire and drums, all have to be designed and added to the store, I havn't read anywhere that said weapons and other store items would be customizable, which is a shame but, I'll love the game anyway. Plus their gonna have to create alot of pre made creatures to populate the universe so that it won't be lifeless at release. Wouldn't that be fun

, just sitting around making creatures and getting paid

.... I wish I had that job.
Anyway, while alot of the content will be player made, I'm sure their will still be alot of Maxis-made content as well.