It’s true that the great Kosher delis are all gone. When I was a kid, I would work sometimes at the Rialto deli on Broadway and 48th St.
[You can see the outside of this deli in the movie, ‘A Fine Madness’ with Sean Connery, which was just released on DVD (although I haven’t actually watched the DVD). The inside of the deli shown in the movie is a hollywood set – the real one was too small to shoot in. ]
At any rate, they used to pickle their own corned beef and cure & pepper their own pastramis in the basement. No deli does that anymore. They’re all made by outside services. Likewise, almost all hot dogs (aside from Hebrew National) sold by New York restaurants, are made by the same company (I forget the name.) The might use different recipes for each restaurant, but the meat used is essentially the same.
There are a number of reasons why there are few Kosher delis left and whether you want to accept it or not, these types of restaurants are going away. For one thing, the number of Jews in NYC is actually decreasing. For another, most of the food is not very healthy. It might be delicious, but it’s not healthy, although I think it’s fine to eat once in a while. And while New Yorkers are pretty diverse in their food tastes and their desire for ethnic food, I don’t think that Kosher deli type food is in big demand any longer.
Katz’s is not a true traditional deli. It’s not because it doesn’t have a full family menu, as others have suggested – it’s because Katz’s is not a kosher deli. Even Berger’s is no longer a kosher deli and it’s right in the middle of jewelry exchange district where thousands of hasidic jews work.
But there are still a few "pretty good" delis left in New York. There is Arties Deli on Broadway and 83rd st. Their pastrami is pretty good, but it’s not hand sliced. My favorite and still-kosher New York deli is Ben’s Best in Rego Park, Queens. (It has nothing to do with the Ben’s chain.) I think it’s probably the best kosher deli left in NYC. Their brisket and their pastrami is really terrific and their turkey breast is pretty good as well – much better than the turkey breast at the now-gone 2nd Avenue Deli, which was always dry and tasteless.