Not only do good standards allow different computers to communicate,but they also increase the market for products adhering to the standards. A larger market leads to mass production, economies of scale in manufacturing, better implementations, and other benefits that decrease price and further increase acceptance.
Standards define what is needed for interoperability: no more, no less.
Similarly, a protocol standard defines the protocol over the wire but not the service interface inside the box, except to help explain the protocol.
That said, good service interfaces, like good APIs, are valuable for getting protocols used, and the best ones (such as Berkeley sockets) can become very popular.
Standards fall into two categories: de facto and de jure....De facto standards often evolve into de jure
standards, especially if they are successful.