Seems Mr Google and his Analyticks are more accurate* than more than one J Random USAnian**.
* Yorkshire
** Australia
I got asked if I was Australian on a number of occasions traveling in Canada and Alaska. I put it down to a decision process of: Speaks English => Doesn't speak like royalty => doesn't sound cockney => must be from another English speaking country => Probably Australian...
TBF, I wouldn't be able to differentiate between people from widely spaced parts of North America, either.
That survey, though - what tosh! I hail from the same neck of the woods as Ian, and have a North Notts/South Yorks accent (only slightly diluted by 20 years in South Wales!). The survey's conclusion? West London.