Part of the reason Microsoft has 'slumped' is that it started paying dividends. It realized it got all the market share it could, and became a blue chip. Apple also started paying dividends, so this is a real possibility. Of course, it is no way a sign of failure.
I would say the reason Microsoft slumped was that they lost the main driver of their innovation, Bill Gates. While this article (http://www.zdnet.com/blog/btl/chart-microsofts-performance-u...) is a bit old now it shows pretty clearly a difference in Microsoft's performance before and after Gates.
To me it's the same question that has to be answered for Apple. Will Apple post-Jobs, be able to keep performing? We'll find out in a couple of years, but it is possible that the issues with Apple Maps, Siri and iMessages are a sign of the pre and post Jobs eras. I contend that Apple would not have released any of these products in their 'beta' states if Jobs were still CEO. It is that type of sloppiness that could keep them from reaching $1 trillion and falling from grace.
