alt Hacker NewsBrits will either say "Fine, thanks" or not respond at all. Poles will tell you that yesterday they went to visit their relatives, and now they're tired, or that their cat is sick, or that they having problems with something.
It's a difference between "asking when you don't care about response" vs "asking because you genuinely want to know how the other person is"
In the UK, a perfectly valid answer to "How are you?" is "How are you?"