Well, you might say that Jewish people were unique in the way they were treated over thousands of years, that their society-within-societies was unique, and that the inward-looking nature of their humour is a reflection. And that is why, perhaps more than other nation/race, the Jew is made to be the centre of the joke.

Reversing the proposition for the moment, like many schoolboys I was brought up on the "There was an Englishman, a Scotsman and an Irishman" joke set - some of which I can, unfortunately, remember over 50 years later! However, recollection tells me that, in many of these jokes, the Englishman came out top and the butt of the joke was the Irishman. Another cultural viewpoint and reinforcement? Or were they just told to me that way... :-)