Apple is certainly going to continue making a lot of money from the iPhone but they haven't innovated a single thing since the iPad. Actually, they've been playing catch up on pretty much every single front and they are still way behind on quite a few (e.g. wireless charging, NFC, ...).
It is highly unlikely the current #1 will not be #1 forever.
I guess the question for investors is is could Apple loose market share in the future in the same way Blackberry or Nokia did in recent history?
Kimberly Clark is an extremely diversified company in the home goods and HBA market. Some of the brands they own:
Kleenex, Scott, Huggies, Pull-Ups, Kotex, Poise and Depend
Imagine that its 1984 and you've just used the same argument, substituting 'IBM' for 'Kleenex'...
Per this 2011 article (http://www.nytimes.com/2011/09/28/business/media/researching...), Kleenex has a 47.1% share of the facial tissue market. I assume these numbers reflect the U.S. (rather than global) facial tissue market.
Per this recent article (http://www.macrumors.com/2015/09/03/iphone-us-market-share-c...), Apple has a 44.2% share of the U.S. smartphone market.
Although the text of the article doesn't say it explicitly, the title of this article effectively screams "Apple isn't well diversified! Its making too much money on one thing!" I really don't see the sky falling here by any means. Barring a seismic shift in the smartphone market, Apple will continue to dominate the smartphone market, making obscene amounts of money; they will probably also continue to innovate. And Kleenex will continue to dominate the facial tissue market.