HTML is a hypermedia format. REST is an architectural style that requires hypermedia in order to work. Hypermedia formats have factors (http://amundsen.com/hypermedia/hfactor/) that make them more suitable for some use cases and less suitable for others. HTML alone does not have idempotent updates (PUT, DELETE), but as REST allows for "Code-On-Demand", we can augment the user experience with Javascript, and it allows PUT/DELETE (with XMLHttpRequest).