Well, "reliability" can be sliced in a couple of different ways since that term can cover both the A & P in the CAP options and it can also mean the elimination of single points of failure and an architecture that can degrade gracefully when components fail. Some NoSQL systems let you select the mix of consistency and reliability you need at a rather fine-grained level -- one thing that does distinguish these systems from the traditional RDBMS is that you are almost never in an all or nothing situation regarding any particular part of the data space unless you explicitly want to create that choice to enable other options.