If you define "core competence" sufficiently vaguely then sure, everything can be related to that core competence.

"a logistics business, both information and physical"? Really? Calling their massive retail business, original content, and physical devices an "accessory" to their warehousing is an extremely myopic view of Amazon.

Remember that much of what is sold on Amazon.com is not actually sold by Amazon. Amazon provides warehousing and fulfillment and an online storefront for third party sellers as well as for itself. The tools that it uses to run that online storefront in the form of AWS are used by many non-Amazon websites as well. The Kindle ecosystem helps Amazon sell retail books but also provides a self-publishing platform. It's not unreasonable to say that logistics, warehousing and web services are the real business, and that Amazon's retail business is one of many customers.

Might as well call Apple an "electronics business, both small and large."

Amazon sells retail themed logistics. Apple sells consumer computing themed user experience.

What does Yamaha sell?

Nothing, business. It's a conglomerate. A business that's function is running businesses. A Yamaha piano has nothing at all to do with a Yamaha motorcycle exactly opposite to how all of Amazon's services are related and intertwined.

Steve Yegge's Platform Rant is still relevant, I think.

https://plus.google.com/+RipRowan/posts/eVeouesvaVX