It's astounding how poorly the market understands Apple. They're completely oblivious to the real issues that are limiting Apple's growth (constrained supplies of key components), and pay far too much attention to market share.
For most devices in most quarters (aside from those in which a major upgrade to that device is introduced), Apple doesn't tend to have shortages, so it doesn't seem like their growth is being significantly constrained by component supply.
Maybe, but I think it can still be an issue, e.g. they release a new product now, and stock is constrained so they can't sell as much as they like. Now, this is the Christmas quarter, so many people will be buying something. If they can't buy an iPad mini now, and they buy a Nexus 7 instead, it doesn't matter that they could then buy it in January. That's still a lost sale to Apple.
Component shortages can manifest themselves in different ways too, e.g. why doesn't the iPad mini have a retina display? Is it because of display shortages, or processor shortages (non-retina means they don't need to put an A6/A6X in there)? It's arguably not because of profit margin: the Nexus 7 has an almost-retina display at a fraction of the retailing price.
