I read the original USA Today article when I was away last week. I would certainly agree that J class service, especially short-haul, is not as attentive as it might be, although for most international flights I have been well treated.
With respect to dress codes and the "kind of people" who are in the front cabin, I must admit that I do tend to take a little more care to look respectable when I'm likely to be flying in J. It makes me feel better. But it doesn't really bother me how others dress, as long as they are polite. The lack of "class" in J is by no means restricted to the jeans and t-shirt set (in fact, the contrary is more likely to be the case).
Without prejudice, I wonder what kind of passenger Joan Rivers might be.