I think it is a mistake to equate "relying party" with "client". These are two different concepts, and the first term is relatively poorly understood among computer professionals (or at least unfamiliar to many of them), while the 2nd isn't. Anyway, back to the difference. A relying party relies - it acts on some assertion. A client consumes - it just takes the stuff it gets from the big producer (the server). There are times when we are clearly talking about an OCSP info consumer and not talking about the decision that the underlying system will make based on that OCSP info. Also, it is somewhat inappropriate to describe the OCSP client as the relying party, since the RP can chose to ignore the information if it needs to, based on some other criteria.