https://www.cnbc.com/2017/11/03/apple-ceo-tim-cook-why-we-had-to-stagger-iphone-x-and-iphone-8-launch.html

The dual September unveiling of the iPhone 8 and iPhone X, but staggered release dates, was borne out of necessity and not "marketing," Apple CEO Tim Cook told CNBC after reporting blowout quarterly earnings.

"If we could do anything we wanted to, we would have obviously shipped 8, 8 Plus and X on the same day," Cook said Thursday evening in an off-camera interview. "But we felt like the most important thing for us to do was to announce them on the same day so we wouldn't have customers buy an 8 and then we announce the X and ship it and they go, 'Oh, you hosed me, I would've bought a X.'"