You can just snatch things off the shelf but it will be a tad bit unrealistic if there are no consequences. I've heard rumor of them adding a crime system after release.

Just a guess, I believe they want to avoid unnecessary complexity in hopes for a good launch, for many of the more elaborate TES features we have a "maybe after release". I understand this as an attempt to remain staying on the safe side of things, as far as tech goes.

I believe they've said it would come with the thieves guild expansion/update, which is after launch.