In B2B and in the enterprise world in general SOAP is often the top choice. The advantages for SOAP often mentioned are:
- Type checking (via the WSDL files)
- Availability of development tools
- Lightweight and easy to build
- Human Readable Results
In Health Care, SOAP is still widespread and prevalent. However there are some interesting projects such as NHIN Direct Health Information Exchange where the relevance of REST vs other API protocols are discussed.
It will be interesting to see what will be the outcome of such discussions.