I think you meant "<My country> is the default on the internet. So unless explicitly mentioned I tend to assume content is geared to a US audience." Because you are American and you tend to visit US-centric sites. No shit.
I am pretty sure 90% of sites visited by Chinese citizens to be hosted in, and tailored towards China.
Also it's not just the Internet being US centric. It's American people being US centric in general, and thus on the Internet make it seem like only US exists. It's more cultural than you think it is.
The US has a larger population than the entirety of western Europe and it's easily the largest western country. I'm not from the US and I'd still consider it the default by sheer size.
I agree with your assessment.
I am not US American though. I live in America (Canada specifically) but I was born and raised in Europe. I'm afraid the cynicism in my original comment requires this context to be received.
In my opinion it seems to reflect an expectation in culture in general. Most movies filmed in Canada do not actually depict Canada. I lived in Toronto for a while where there are almost as many NYPD cruisers as there are TPS cruisers and as many Yellow Cabs as there are Beck Taxis. International YouTubers translating things into Imperial Units and US Dollars in videos is another often seen accommodation to this.
I think my simplest heuristic for agreeing with your point is how much content there is in the English Wikipedia vs. other languages. I haven't run the numbers, but I'm sure it's also much more US centric (take a look at the # of articles on the US government (current and historical) vs., say, the Brazilian government...)
America just tends to be particularly prolific in producing online content. No, I'm not claiming this as a statistical fact, but I am claiming that's the impression day in an day out so might as well assume as much...
I am pretty sure 90% of sites visited by Chinese citizens to be hosted in, and tailored towards China.
Also it's not just the Internet being US centric. It's American people being US centric in general, and thus on the Internet make it seem like only US exists. It's more cultural than you think it is.