Yes. And without over stating it, iOS is an amazingly robust, very secure OS. it has high trust and low trust models, a secure zone, special purpose hardware and an operating system designed around minimum access rights models which manages to keep going, despite app authors worst intentions.
At one level, it proves the model. The shame is that Mach otherwise has kind of not taken off. Gnu the OS was going to be Mach at the core, at one point IIRC
