This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Obviously, I think you can build services using a variety of frameworks, and so SCA is certainly not a requirement for SOA. That said, I think SCA has some very compelling features as it relates to assembling services through reusable components; supports a broad-range of bindings so that services can be exposed over SOAP, REST, JMS, ESB, RMI, RSS/ATOM, JSON etc; and has a powerful distributed deployment model. I don't think SCA is all that complicated to get started with, and hopefully my book addresses that through its case studies and examples.