Hmmmmmm.....
So -
1) Android is going to end up on a lot of phones - basically the none Apple ones. Microsoft is going to bob along at the back with a small amount of market share.
2) Apple's computer business is based on having the majority of the high-margin business. Most of the PC business is selling a wafer thing margins.
3) Apple caused/prompted a massive take up in smart phones and tablets that spread usage of both a long way outside the usual niches for such products.
4) Everyone else is following the Apple lead in these two areas.
5) It is assumed that Apple won't make a mid/low price offering in these two market areas. But what did they do with iPod?
All of the above strongly suggests that Apple with be a declining percentage of the phone/tablet market. But they will probably have quite a lock on the high-margin part of the business, and probably record massively growing sales in absolute terms for the next few years.
As tech marches on, there will be point where iPhone/iPad "Mini" offerings will make sense - sufficient performance on a cheaper device. We have also seen, to date, the results of attempts to build cheapo tablets...