Create-a-World was free, and people made worlds for free (I helped contribute to projects like these). The Sims 3 Store Worlds were Official content, and at this time they haven't mentioned "Makers" would have access to a CAW tool. And if they do, and charge—think it will ruffle feathers.
I don't care if official/Maxis content releases worlds and I might even buy them, but if "Makers" do I won't buy (because CAW should be free).
Plus, from what I remember one of the redeeming factors of the Sims 3 Store was the ability to gift to people, that isn't available (at least atm).