I think there's a lot of factors in play, and probably more than I am aware of. The first one I can immediately think of is that ads are quite often not served

I think there's a lot of factors in play, and probably more than I am aware of. The first one I can immediately think of is that ads are quite often not served worldwide. I only started receiving ads very recently, first only a couple but now there's an actual variety. I also started using adblock recently :) The next one would be the content consumed. While Facebook is pretty ubiquitous, other countries have their own social networks which may have less common or less intrusive ads. Similarly, other countries would consume local news/blogs/etc, which might have the same characteristics. As an example there, visiting NYT/Forbes/HuffPo/etc always gives me a headache(pre-adblock), but our local online newspapers use fairly light and simple banner ads. The third one would be the level of tolerance for ads. As American media seems to blast ads at a very high rate, American users may have grown extremely intolerant to them. I don't mind our own ads that much, which are comparatively sparse and much less 'attention-grabbing'. Of course, over time, I've grown less and less tolerant(I've already stopped watching TV), but averaged over a whole population there's probably a notable difference there as well. All three of those reasons also touch upon a pretty central one - the type of ads being served. The more obnoxious the ads, the more likely people are to use adblock, and there's definitely a difference in the "advancement" level of ads in different countries.