Apple's strategy seems to be investing in a few features that matter, and blowing it out of the park when they are released. They focus on ways to improve user experience and For example: Retina displays. Manufacturers kept trying to improve screen size and resolution, and then Apple trumped it all when they introduced the Retina display. Now you can't really compete w/o offering as good a ppi on your LCD's. And you also can't practically compete by offering a higher one (looking at you RIM), because you can't reasonably tell the difference. You are reduced to hoping your customers are idiots if you do this.
Combine this with very good UI/UX (mostly UX, and it could be better, but it seems no one wants to go there) and you have the current situation of an almost unbeatable device with everyone else fighting for second place. Who cares if Android can do "everything and anything," if I am slowed down by its UI, or it works inconsistently. An android phone/tablet's only markets are: budget purchases, people who don't have an iPhone, and people that don't mind dealing with Android just to have a specific feature they actually need, or just to not have an iPhone. Is Android taking market share? Perhaps, but I suspect only related to those three sections.
Apple's recent switch to selling yesterday's hardware at a lower cost isn't helping the competition much either. They release a new plate of devices at intervals while killing the previous models. That means there are no new, cheaper devices on the market for that company. Apple will sell you a new yesterday iPhone, at a cheaper price, and support it.
Amazon recently has 'gotten it' as far as customer experience goes. They provide excellent services that tie-in to their Kindles, support the older hardware, with the bonus of doing it cheaply. Since Amazon sells services, they can afford to subsidize the hardware with the intention of adding additional subscribers. They also sell a specific user experience: convenient and pleasant reading (and more recently, additional Amazon services).
What do competitors offer against these two other than catching up? Almost nothing. They add features, but only as growing lists in hopes that people will buy the device that has the largest one. Perhaps this is the reason every eReader is a Kindle for some people. And every tablet is an iPad. And every smartphone is an iPhone.