WCF was introduced as part of ASP.NET 3.0/3.5. The greatest enhancement and reason for change was around security. With this in mind, many of the SharePoint Web services are still traditional ASMX Web services, though some like ListData.svc, which take advantage of WCF, have been added.
For a discussion on traditional ASMX Web services in SharePoint, see Chapter 19.
It should also be noted that when working with ECTs you can only configure WCF Web services and not the ASMX type Web services, such as those discussed in Chapter 19. When trying to discover the type of web service you are working with and its validity in configuring BCS Web service connections the file extension SVC indicates a WCF web service and one suitable ...