Zemanta's API is one of them. We're not dealing with resources, we're dealing with analysis of text (natural language processing, information retrieval, etc...), so except of the basic url scheme, there's not much that you can take from the RESTful idea.
You could just POST the text, get back a bunch of links to the resources and then GET the ones you're interested in.
Assuming that certain "objects" are more expensive than others to generate, a resource-based view with lazily-generated representations could be more efficient than wasting resources without knowing if the client needs them or not.
What's expensive is the analysis of the original text, not creation of the objects. If you want to do what you are saying you would need to create and store objects server side in order not to have to re-do the analysis the second time around. There's no point in that.