Apple had most of the OS in place when the project began. That's why, to this day, a bunch of iOS APIs start with "Nx."

Also, the reason the App Store appeared overnight was that they had been planning to use it for the as-yet-unannounced iPad all along. It was almost ready to go when the iPhone was announced; all they had to do was pivot away from the moronic "Web apps only" strategy they had been pushing for the iPhone.

So hopefully (for Google) they are in a similar position, with years of work already done. We'll find out.