Web Services are standards-based interfaces to software functionality, while SOA is software architecture oriented toward Services. The definition of architecture is the fundamental organization of a system embodied by its components, their relationships to each other and to the environment and the principles guiding its design and evolution (from IEEE). Web Services alone can reduce the cost of integration, but will no more give you SOA as having a pile of lumber and nails will give you a house. In fact, it's possible to have one without the other -- although building SOA without Web Services will more than likely lead to bad SOA, because achieving loose coupling in the face of heterogeneity is far more difficult without the use of open standards.

Se fosse pra dar um chute eu diria que a construção de Web Services não representa 10% do trampo de um projeto de implementação SOA. Na verdade algumas ferramentas já prometem fazer boa parte do Serviço de forma automática. Em um projeto SOA de VERDADE é difícil fazer tal confusão. Ela existe mais no marketing "cascata" de alguns fornecedores.


Moral da história: "Não confunda alhos com bugalhos".