You can design to minimize P, though. For instance, if you have all the services running on the same physical box, and make people enter the room to use it instead of over the Internet, "partition" becomes much less likely. (This example is a bit silly.)

But you're right, if you take a broad view of P, the choice is really between consistency and availability.

Yes. P is kinda fundamental to your setup.

For example, running S3 locally or not.