That is, we discussed these as stand-ins for hypothetical future methods while discussing the general problem of extensibility. We did not have time to fully discuss caching for PUTs and POSTs. We have to be careful to distinguish between conditional execution of a method, and conditional return of the response. In the case of GET, since it nominally has no side effects, conditional execution of the method is not so important.
Some people believe any response is cachable if it includes the 'right' headers.