I'd say the truth is somewhere in between. Closer to a comedian using another comedian's joke.
Original authors of the jokes either don't earn any money with them or do it similar way that the "joke thief" does. Only they are not that popular as he is.
I think reposting is much less of an offence then one proffessional comediant using joke of another one without proper attribution.
Good point, though. Delivery of embedded content is often ignored.