As smartphones become more powerful, commonplace, and Droid's reach continues to expand, I see Apple becoming less and less relevant over the next decade. iPad type devices will continue to be popular but I don't see Apple maintaining their market share, and the entire thing feels fadish to me.
The iPod is already on its way out imo... except maybe the nano etc for people who need something smaller than their phone while exercising. No one wants to carry around multiple devices and they wont have any reason to when their phone can do everything. You have generations of people replacing their iPods and dumbphones with smartphones, and a vast number of them will not be getting iPhones. I think this will cause a slow but steady migration away from iTunes.
This leaves them with the people who bought an iPhone (this # has been losing ground to Droid devices), iPad, or an Apple Desktop/Laptop. The iPad craze will cool down, their other hardware will continue to be overpriced, and their grip on the online music industry will slip. Obviously I don't see them disappearing or going away without a fight... I just don't see them maintaining the market share they have - pretty much in any category. Their relevance in the bigger industry picture will be minute.
The companies we should be afraid of are the ones that have control over the largest amount of information, personal or otherwise, and I don't think Apple even falls into the top 5. I have no doubt Jobs would like to get to that point though..