I like to look at multi-core CPUs as examples. While in theory cores can partition from each other or fail in myriad of ways the system is engineered such that the probability of these failures is low enough that it doesn't matter. If you lose a core or you lose an interconnect between the cores, you lose the chip. Really you can look at each transistor on a chip (any chip) as a node in a distributed system, as long as the system is engineered not to fail you don't really think about CAP.

The more interesting trade-off is using consensus algorithms for availability and durability. You can keep going as long as you have a quorum of nodes but you pay an extra rtt (at least). Having multiple replicas (in either consistent or eventually consistent systems) costs in linearly more expensive writes and storage (typically, unless you use some sort of erasure coding.)