The "global default" is a good way of putting it. English is, after all, the lingua franca -- a term that originated when all the who's-who of Europe spoke French. What else would you speak?

To answer the question as to whether the US has a culture, all you have to do is to take a US citizen and have them live in another country for a year or so, or become an immigrant to the US. Culture "suddenly" appears as if out of nowhere:

We realize US culture is build on our large landmass with two oceans -- something that drove American expansionism and still feeds in to foreign policy.

Turkey is a meal that means "American" in a way few other meals do.

The US government & judicial system, formed during the age of democracy, reflect the cultural ideals that built the country.

From road trips to Park 'n Rides to takeaways and country music -- even though the US seems to be everywhere in the world, take the American out of the US, or put an immigrant in it, and the culture becomes readily apparent.