Apple has many advantages over competitors. In terms of resources, Apple has a very strong and loyal technology team, which is their biggest asset. They also have many patents, which makes it expensive to develop technology similar to that of Apple. For instance, Samsung is fighting expensive court battles against Apple on patents related to their Nexus tablet in EU.
In terms of core competencies, I see the following as differentiating factors for Apple:
1. Control over whole eco-system: Apple controls hardware, software and apps which go onto Apple's products. Though they allow third-party products, the products have to adhere to Apple's stringent requirements. The main advantage here is that Apple acts as a funnel and has complete control over what the user gets to see and also can monetize it (through a commission), when users purchase things from Apple store.
Another accrued advantage here is that Apple can have the final say on many issues and third-party vendors have little bargaining power with Apple. That's why music companies don't really like Apple, though they earn a lot of money through Apple
2. Tight control over entire supply chain: Apple uses manufacturing units in China, but have complete control over quality and delivery times.
3. Brand equity: Apple has carefully developed brand equity over years and now stands for beautiful design, easy user experience