In particular, it's a very East Coast thing. While we have the mom-and-pop pizzerias on the West Coast, there aren't styles of pizza named for West Coast cities and we just don't have that pizza rivalry that the other coast has. There's California-style pizza, but that's named for a state rather than a city, and as soon as you leave California it's easier to find almost any other kind of pizza.

I disagree with the claim that they are, as a rule, universally applicable, though I certainly do not disagree that this is highly US-normative. There is a significant subset of comics specifically about US issues, stretching back all the way to the very beginning. I can, upon request, provide examples.

1:

known mostly for

[Citation Needed]. You clearly are not a regular reader if you haven't seen his near-constant references to US politics, electoral systems and why the US' sucks, or literally one of the first and most oft-quoted XKCD comics of all time, which only makes sense from the perspective of a country where, even in the 2000's, literalist interpretations of religious texts and anti-science narratives are not just ever-present, but were already one of the primary voting issues for the entire country

2: You are not entitled to an "excuse" for Randall Munroe daring, nay, displaying the absolute temerity to make a comic about pizza. For someone supposedly calling out US-Normativity, you certainly seem awfully clueless about the implicit assumptions you make.

3: I'm sorry that you feel entitled to an apology for an american comic artist drawing a comic about something quintessentially american. I am more sorry, however, for whoever failed to teach you that expecting other people to conform to your normative beliefs when they do something for themselves is a bad thing. He never once said that he would make it non-"US centric". The only promise he has ever made about it is that it is "A webcomic of romance, sarcasm, math, and language." This comic is both sarcastic and related to the semantics of language. That you feel it is too "US-Centric" is your own concern. As a resident of Ameristan, I can say with confidence that you making that normative expectation is the most american thing you could do. Unless, of course, you were eating a weird slice of "pizza" while doing it.