Technology: Choice/Selection
How has Apple become the biggest company in the world?
There have been many factors: Marketing, innovation, and user experience are definitely some of the major aspects that Apple has excelled at.
To me, quality control has allowed Apple to create a brand that is trusted by so many users. Unlike Google's Android and Microsoft's Windows, Apple's software is only used in Apple's hardware (unless it's illegally put on custom PCs). Apple can ensure that all their products are capable of upgrading to the newest and greatest software without relying on other companies. Consumers can be confident that Apple will support their device(s) and offer prompt update for multiple years; that can't be said of all Android devices.
Another way Apple has increased it's marketshare over it's competitors? Selection. Or the lack of.
Though, this is a mistake where I think Apple has been making recently. It was Apple's advantage to have a limited selection; the consumer didn't really have to decide what model to get. It was a simple process. Now, they are selling more models of products than ever. Just look at the iPad: iPad Pro, Air 2, Air, Mini 4, Mini 2. Confusingly, the Mini 3 was discontinued.
For the iPhone, there is the 6S Plus, 6S, and 5S. There is no surprise Apple still carries the 5S for its customers who desire smaller phones. But there will be a time where the iPhone 5S will not be able to support the latest iOS version, essentially removing the phone from their offering. It'll be interesting to see if Apple adds a third version of their latest phone lineup.
For the Macbook lineup, you currently have the Macbook, Macbook Air, and Macbook Pro. Somehow the Macbook Air is heavier and bigger than Macbook. While the selection of laptops is no different than in the past, it is definitely more confusing. There are 2 different sizes of Macbook Air and Macbook Pro; and the Macbook Pro has a version of the 13" that does not contain retina display.
The Apple lineup still seems limited compared to its competitors. Google and Microsoft have individual third-party hardware manufacturers that offer the same or even more devices than Apple. The selection of Android and Windows products are overwhelming; even as an avid technology follower, I can't follow all the laptops coming out from major computer majors. And for the average consumer at a retailer, they see this:

It's no surprise that Apple has increased sales.
With the Surface and Surface Book, Microsoft is following Apple's path by offering a software and hardware combination. It does not surprise me that Google is continually rumored to be creating their own phone; and I think that would be an excellent plan for Google. As for the third-party manufacturers, they'll have to rethink how they present their products (read reduced bloatware, and more useful integrated software packages).