The way I see the reasons is this...
1. There are only two reviews... and a 1 star and 2 star averages to 1.5
2. When viewing the one start reviewer, its the only thing he has ever reviewed on amazon.
3. The 2 start reviewer has reviewed more things and is actually fair and resonable rather than being over negative, like they were insulted by WRML.
4. Most people are skeptical over a newly introduced concept that is not proven or has a huge community around it, especially when it come to passionate subjects such as what makes a good REST design.
5. A lot of people using JSON are afraid that any level of specification used to mature the tooling will render its design inflexible, which is a knee-jerk reaction.
My honest opinion is that there are a number of developers and projects working to address the lack of specification in JSON, and this is one attempt to abstract formats and specifications to make RESTful designs more flexible to changes in both. I'm not sure what attempt will win out, but the gaps are just asking to be addressed to mature REST to another level.
A JSON specification is not an equivalent to
SOAP any more than an IDL is equivalent to CORBA. As long as the REST constraints are held, then it shouldn't matter what format is used to transfer a representation, or even whether there is a specification for it. For example, JSON is still considered more human readable and easier to parse (depending on your message complexity) than XML and adding a specification to describe the structure of its contents does not change its format or use at all.
Beyond the WRML concept (which does not have to be used to apply most all of the practices in this book), there's a lot of good information and practices contained in a concise format (as the 1st amazon reviewer admits). Much more complete than I've found in any other REST book I've read and recommended (i.e. REST in practice, RESTful service cookbook). It makes a good reference when designing a REST system beyond a sample RESTbucks application.
