I don't count that as a positive, since it would at least prevent them from calling it restful.
> The URI is RESTful. (Explicit collection and member actions, with common namespace.)
URIs can not be RESTful, this does not even make sense.
> Supports both JSON and XML. (Internet media types)
Supporting "JSON" and "XML" is completely useless: they're meta-format, in and of itself outputting "JSON" is completely meaningless as it does not tell the client anything.
Defining the exact media types returned (which this API description barely does) is the vast majority of a RESTful application's documentation. In fact, it should be all of the documentation save for a single URL, which is the API's root entry point.
> Bitcoinica API utilizes three of the four RESTful Web Services methods - GET, POST and DELETE. (HTTP methods)
Better, but still not sufficient to make an API restful. Plus orders are created via a POST, that's not correct, the semantics of POST are updating (creation is PUT)
> But I'm not sure about the hypertext part, because I don't understand what hypertext means here.
And you don't think that might be an issue in your judgment?
> Is Bitcoinica's interface considered hypertext-driven?
No, and being hypertext-driven is the most important criteria of a RESTful application.