ur s0 rait, eye d0nt nnno wy ne1 b0dderz tu b3 "proppr"!!!!1!!
</sarcasm>
You are correct that communication is the point. Words do communicate a message. So too does disrespect for propriety: it communicates the message that the person who is ignorant or disrespectful of proper language is either uneducated or immature, and that in turn implies that such a person’s statements and opinions should be discounted if not ignored entirely.
Words and terms mean things. The term ‘REST’ was coined to mean something. I contend that the thing ‘REST’ originally denoted is a valuable thing to discuss, and a valuable thing to employ (I could be wrong, but how easy will it be for us to debate that if we can’t even agree on a term for the thing?).
It’s similar to the ironic use of the word ‘literally.’ The word has a useful meaning, there is already the word ‘figuratively’ which can be used to mean ‘not literally’ and a good replacement for the proper meaning of ‘literally’ doesn’t spring to mind: misusing it just decreases clarity and hinders communication.
> If my API is supposed to rely on content-type, how many different representations do I need? JSON is a given anymore, and maybe XML, but why not plain text, why not PDF?
Whether something is JSON or XML is independent of the representation — they are serialisations (or encodings) of a representation. E.g. {"type": "foo","id":1}, <foo id="1"/>, <foo><id>1</id></foo> and (foo (id 1)) all encode the same representation.