It depends how you define Christianity. As I said before, people in America seem to have a certain preference for their own culture, which has been influenced by a form of Christianity. That doesn't mean that voting for politicians who market themselves as Christians is actually a vote for "the God of the Bible", though. It could equally be a vote for generic white middle-classness, or for not-a-foreigner-ness, or not-Muslimness, or unlikely-to-rock-the-boatness. Or even, in a few staggering cases, because people thought the candidates were good and liked their policies.
Certainly I imagine most people would be anti- my particular view of God, ie the Calvinist one, but I think it's a broader issue than that. I don't imagine most people, if pressed, would accept most
of the generic characteristics of God as agreed upon by all sorts of denominations. It goes against a lot of modern thinking. God's omnipotent? Problem of evil/He should have saved my grandma's life/but what about earthquakes? Omniscient? Free will. Holy? There's divinity in everything (or nothing, perhaps). The Creator? Evolution. Wrathful? But I don't deserve judgment/man's basically good/that's not fair. Described in predominantly male terms? Sexist. And so on. "Loving" would probably be accepted, in a vague sort of way, but that might be about as far as you'd get.
So I do think it's good that "Christianity" as a phenomenon - from potluck casseroles to hate marches - be separated from Christianity - any and all versions of it - as understood on a doctrinal level. Preferably by discussion more nuanced than the quiz in question.
I think Christians do tend to view this differently than non-Christians. I'm sure it would be much harder to be a Muslim or Buddhist in the USA than a Christian, in terms of persecution and prejudice. But perhaps non-Christians are more willing to lump cultural Christianity in with the real thing than practicing Christians are. (Just as, I'm sure, Christians in Iran are likely to conflate religious and cultural Islam.) As a Christian, I tend to view claims that companies, politicians, individuals etc are Christian with a degree of cynicism, just because the term's so often co-opted for political reasons or out of sheer laziness. I mean, I won't tend to challenge people on it, but if they want to convince me they have to do more than just use the buzzword.
Whereas if someone told me she was Hindu, I'd tend to assume she was a "real" Hindu, because I have less familiarity with the ins and outs of it - whether or not she was practicing it according to its tenets, how much social pressure she had to call herself one, etc. It's not the language I know, if that makes sense. And I wonder sometimes if non-Christians do the same thing to Christianity, giving them a rather distorted idea of what the religion actually entails (ie. "They must be Christians, they eat tunafish casserole!"). Does that make any sense?