With all the hype about Apple right now it hard to even think that they will one day fail!
But I too belive this powerhouse will fall. The open source ecosystem of the WWW is just the norm. Sure it seems cool to have a propiety Apple tablet and phone, but you can no win against the numbers. The number of people who support and work on open source just because they can and want to make a software perform better and more functions is only measurable to the close source platforms.
So while Apple is on tp today I will bet against them in the next 5 years. I think they will succumb to the open source or die model.