I still don't understand what you mean when you say, "probability of remaining consistent," etc. Either you wrote the service so it system would always remain consistent or you didn't. Similarly with availability. Either the system will always return a result, or it may sometimes hang.

Maybe what you mean is the probability of whichever of C, A, or P you gave up actually becoming a problem? But I cannot imagine a physical law of the form you are referring to applying uniformly to these disparate properties. I wouldn't even know how to formulate it for consistency. For availability and partition tolerance it would just be, "Requests to this service will (availability: hang forever/partition-tolerance: return with errors) at a rate exactly equal to the probability of network failures."

With regards to your last point, there are no reliable networks, at least where I work. That doesn't mean there won't be.