Originally Posted by Adraco

For Windows, it had something to do with the number 9 being used as a stop variable, indicating the end of a series.

For Apple and iPhone, I think much had to do with it being 10 years since Steve Jobs introduced the iPhone. That's why Apple announced the iPhone X in the "Steve Jobs Theatre" in their new headquartar that he started to build. That auditorium has not been used before and had its first use yesterday with the memorial of Steve Jobs as opening number. A very nice way to pay tribute!