The UK is geopolitically in Europe. That is a simple fact, the same as Canada is in North America. That some people in the UK choose to refer to the European mainland as 'the Continent' or 'Europe' as distinct from the UK is a separate matter. Some people also refer to anything east of Greece as the Orient, or to Africa as the Dark Continent.
Nevertheless, the point irishguy28 was making, I believe, is that my assertion that Amex is widely accepted across Europe was an extrapolation based on my stated location as the UK. In other words, he was arguing that, simply because Amex is reasonably widely accepted in the UK, it is incorrect to make the assumption that this translates to wide acceptance across the European mainland. As I subsequently noted, in my experience across many European countries, I get along with Amex just fine.