They have invested in future product categories, the Apple Watch being the most recent - and not very successful - example.

I'm afraid what Apple is doing is purely looking at figures - if it doesn't sell at least X or account for Y% of revenue, it's discarded. AirPort, gone, displays, gone, 17 inch MBP, long gone.

And yet their R&D budget is still going up (http://cdn.macrumors.com/article-new/2016/05/Apple-RD-Spendi...), estimated to become $12 billion in 2017. IDK where it all goes though.