Just playing devil's advocate here. I don't really think we all have 100kW batteries in our P85Ds. But...
...If we did, there could be reasons to not advertise it at the launch.
Tesla was already going to sell every P85D it could manufacture. There was no need to increase demand. Think of the marketing hype if they could now come out and say, "Guess what--those cars we've been selling with 85kW batteries really have 100kW batteries. That's what we do. We always under-promise and over deliver. When you buy a car from Tesla, you know you'll always get at least what you pay for, but you never know how much more we might give you, as a bonus."
Can you imagine what the press would be like? And what something like this could do for future sales, when Tesla is not production-constrained?
Again, I'm not saying this happened. Just giving one reason why it wouldn't have been a ridiculous idea to not announce at launch.