This analysis of Amazon's RESTfulness is very good and somewhat eye-opening.
I think this shows two things - organizations can get real benefits from REST even with a partially 'conformant' system and that there is still a lot of room for education regarding what HTTP can do.
I have a feeling that the particular use case that Amazon's system was designed to support is not so much as full automation by any kind of client application but rather it is focused on specific rendering and XSLT style client usage. If an XSLT engine has a hard time integrating then the HTTP usage would be simplified to fit.