Probably, but I see it as a much more gradual decline, taking many years.
Unless they have a new Steve Jobs hatching in some cloning facility, Apple is now being led by the same kind of people as every other large electronics company.
Their post-Jobs momentum will keep them going for a long time, but bigger iPhones and faster iPad processors will just match what the competition is doing.
Do they have someone there with both game-changing new ideas and the single-minded drive to bring them to market? Probably not.
Just being Apple won't be enough, just as it wasn't in 1985-1997 under John Sculley, Michael Spindler and Gil Amelio