This article says Apple is incorporated in Delaware? http://www.nytimes.com/2012/07/01/business/how-delaware-thrives-as-a-corporate-tax-haven.html
That article is incorrect or unclear. They are registered in Delaware, but are incorporated in California. From Apple's investor FAQ page:
When was Apple incorporated?
Apple was incorporated in the state of California on January 3, 1977.
http://investor.apple.com/faq.cfm