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The recognition of SOAP (Simple Object Access Protocol) as a protocol implementing web services stems from its foundational role in allowing applications to communicate over the web. SOAP provides a standardized way for different systems to exchange structured information using XML for message format, and it typically operates over protocols such as HTTP or SMTP for message negotiation and transmission.

SOAP defines a set of rules for structuring messages that can be sent between applications, and it also provides a mechanism for defining the way services should communicate with one another. This includes concepts such as service definition, message construction, and error handling, which are essential for ensuring interoperability between diverse systems and platforms.

While other protocols like XML-RPC and REST also serve the purpose of enabling web services, SOAP stands out due to its extensive capabilities, including robust messaging patterns and built-in error handling. HTTP, on the other hand, is primarily a protocol for transmitting hypertext and enables web communication but does not specifically focus on web services in the manner that SOAP does. Each of these protocols plays a role in the domain of web services, yet SOAP is specifically designed for this purpose, making it the most appropriate answer in the context of implementing web services.