Dude is a constant game changer.
When the iPod first came out there were already other MP3 players, but along with iTunes and the music store, he sold the whole package and changed the way music was sold.
The first iPhone didn't even do half the stuff the Blackberries did, functionally speaking, but when they launched the app store and 3rd party development (for $100 for the dev kit, unheard of at the time), they changed the mobile landscape.
When the iPad came out, there were already other tablet PCs out there running windows, and a lot of people thought it was going to tank (you can probably find 1000 articles on "why tablets won't catch on" before the launch). Not only it caught on, every other company jumped on the wagon, and tablets have been eating at netbook and PC sales like nuts.
He's a ruthless asshole when it comes to the business side, but the way he affected technology is really non-arguable.