Cook is an operations genius, apparently. But he doesn't have the charisma and vision and panache to broker the deals that SJ did for Apple.
I imagine things getting a little tougher on this front for Apple, but otherwise, they have plenty of momentum and a solid culture to run with far into the future.
I hope the best for SJ and was saddened by the news. What a legend.
You know that's what they said about Bob Iger when he took over Disney after Michael Eisner. But the decisions he made and deals he brokered (e.g. Pixar) revitalized Disney. Here's one article of many.
Tim Cook has already been brokering great but inconspicuous deals managing Apple's supply chain. He may not have the big-stage charisma that SJ has but I guarantee you, you do not get to be a successful negotiator (and leader, by the way) if you don't have charisma. I suspect TC's charisma is on a more personal one-to-one level and the chatter I hear on the net seems to confirm that.