)what, historically, have been apple's competitive advantages?

Competitive advantages of apple were; 
Apple preferred Horizontal and vertical integration around its products instead of licensing it or making it open market or sharing the technology.
Easy to use- they focused on ease of operation and simple user interface.
Facility of plug and play so that non-technical users do not face any issues.
Uniqueness and innovation in enhancing consumer's digital life for example- Digital Hub- an advantage for consumers who were becoming entrenched in a digital lifestyle, using digital cameras, portable music players and digital camcorders and mobile phones.
Investment in R&D brought the key competitive advantage to apple.