posted 14 years ago
HTTP is just a transport mechanism for otherwise largely unstructured data. SOAP is an XML format that makes it much easier to add headers, meta-data and structured information, like the ones used for WS-Security and other SOAP extensions. Also, SOAP is a data format, and can exist without there being an HTTP connection.
If you think SOAP introduces too much overhead, check out RESTful web services (which are closely bound to HTTP, and don't provide everything that SOAP does, but which work well for many applications).