If you are a SOA enabled enterprise application vendor trying to sell SOA to your customers you quickly realize that very few customers are interested in buying SOA by itself. Many customers believe SOA investment to be a non-differential one and they compare that with compliance – you have to have it and there is no direct ROI. A vendor can offer ROI if the vendor has the right integration and interoperability strategy. For customers it is all about lowering the TCO of the overall IT investment and not about looking at TCO of individual applications. SOA enabled applications with standardized, flexible, and interoperable interfaces work towards the lower TCO and provide customers sustainable competitive advantage. Generally speaking customers are not interested in the "integration governance" of the application provider as long as the applications are integrated out-of-the-box and has necessary services to support inbound and outbound integration with customer's other software to support customer's vision of true enterprise SOA.
It has always been a long debate what is a good integration strategy for SOA enabled products. Organizations debate on whether to use the same service interfaces for inter-application and intra-application integrations. Intra-application integration have major challenges, especially for large organizations. Different stakeholders and owners need to work together to make sure that the applications are integrated out-of-the-box. It sounds obvious but it is not quite easy. In most cases it is a trade off between to be able to "eat your own dog food" by using the published interfaces versus optimizing performance by compromising the abstraction by having a different contract than inter-application integration. There are few hybrid approaches as well that fall between these two alternatives, but it is always a difficult choice. Most of the customers do not pay too much attention to the intra-application strategy, but it is still in the best interest of a vendor to promote, practice, and advocate service-based composition against ad-hoc integration. There are many ways to fine tune the runtime performance if at all this approach results into performance degradation.
The other critical factor for ROI is the interoperability. The internal service enablement doesn't necessarily have to be implemented as web services, but there is a lot of value in providing the standardized service endpoints that are essentially web services that have published WSDL and WS-I profile compliance. The interoperability helps customer with their integration efforts and establish trust and credibility into the vendor's offerings. I have also seen customers associating interoperability with transparency. Not all the standards have matured in the area of Web Services and that makes it difficult for a vendor to comply to or to follow a certain set of standards, but at the minimum vendors can decide to follow the best practices and the standards that have matured.