George, as well as his parents, are stereotypical of a certain kind of jewish family. If you didn't know his last name, you might assume that they're trying for the whiney jewish gag.
But they are the Costanzas, which sounds hispanic or italian to me. Of course you don't have to follow the stereotypes all the time, and perhaps Seinfeld is making an effort not to. If that's what they're doing, then I'll applaud them.
Maybe there's some other explanation. What's your take on the Costanzas?
PS What about Elaine's ethnicity? Is her name Benez? Pronounced BENez and not BenEZ? Hmmm