Those companies don't need third parties to develop anything so why would we know? Facebook was building custom server hardware for years before it became public knowledge that they were doing it.
You're right — we don't know. That gives us two options. Either we acknowledge the innovations we do know about and have proof of, or we use wild guesses and assumptions to dismiss those innovations.
I'll be happy to praise Google or Facebook for advancements in CPU tech if and when they show us such a thing. Until then, publicly available facts are that Apple is innovating in that field and they're not.
The very fact that we can't tell shows that this isn't any significant innovation. Even the part about handing out dev kits doesn't actually show anything - using an off-the-shelf ARM would create the same impact.
They're designing CPUs - something that many companies have done and many companies will do. Big whoop.
