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> No it's not. In theory, you can just consume the WSDL and have all the methods available to you, but in practice, there are huge and unbridgeable issues with interoperability. A C# SOAP client will have trouble consuming a Java WSDL, and so on.

This is something I have a hard time understanding. Your hypothetical generic REST client will have a hard time understanding my HATEOAS, discoverable, fully REST-ified service, if it has no idea what the service is supposed to do contextually. If my 'blog' resource has links to 'metadata' and 'related' things, without knowing what those are, how does a 'generic' REST client do anything with them?

How is that significantly different than SOAP?

I would love to see an actual example of the difference, rather than abstract discussion, as this is the point I have the hardest time understanding.

The only difference between REST-in-practice-today and WSDL is that you aren't expected to map each network interaction to a single procedure call. This makes a number of things easier: cache the results, GET data across many different endpoints if you know the format, enable data and metadata extensibility through the payload, and follow hyperlinks if you know the link relation and target format.

The Facebook Graph API is a great practical example of this ease of use in practice: https://developers.facebook.com/docs/reference/api/

You're quite right that things like "related" and "metadata" link relations mean nothing if you don't know what those mean - they are hooks for future bits of agreement. The difference between REST and WSDL in the long run, in my opinion, is the practical composability of small bits of agreement (or specs). The Web Services stack (SOAP, WSDL, WS-*) has had a very difficult time composing a bunch of specs together as the kernel of their agreement is basically the XML Infoset. With the RESTful Web, the kernel is HTTP, URI, and MIME (for now), which has endured a number of extensions (Flash, HTML5, Atom/RSS, etc.) and evolutions (the rise of mobile devices).

Caching at the architecture level has caused more problems than it has solved. How many times have you heard the phrase "empty your cache, then try again..". Utterly stupid. This is an optimisation that should be implemented by the application designer as needed, and if it is within their capabilities.

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