Most strips are based in one country or another, and heavily reflect current events, politics, entertainment, and so forth unique to that country.
I'm sure there are plenty of Americans who are not actually getting Andy Capp every time.
Regardless if that question is rhetorical, yes, Americans are that "polarized". I use quotes because, I feel that it is due more so to ignorance than choice. As an American, I don't think the general population truly knows that political parties exist outside of Democrats and Republicans. Most Americans probably couldn't tell you what sort of government the US even employs (hint: it is not a democracy).