This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
As there is no standard definition of "tightly/loosely coupled", it would be easy to argue that both are tightly coupled, and it would be easy to argue that both are loosely coupled. I'd say that SOAP is more tightly coupled than REST because it specifies the data types to be used, whereas REST does not. That makes it a bit harder (but by no means impossible) to change the implementation without also changing the interface.