Answer:
Because London is a big place, and you need to be rich to live in certain districts. Plus you could be talking to someone who lives not that far away, so maybe you will have something in common with that Londoner. If in reply to their question you answer Knightsbridge, South Kensington, Chelsea, Belgravia, Mayfair, St. John's Wood, Primrose Hill, St. James, Holland Park, Regents Park, or Notting Hill; you are telling people you are rich. You need to be rich to live in districts like those, just like the New Yorker who lives in Upper East Side. If your answer to their question is Tottenham, Wood Green, East Ham, Stratford, Dagenham, Barking, Canning Town, Hounslow, or Woolwich; you are telling people you are poor. Very few rich New Yorkers opt to live in the South Bronx. Likewise people will take it to mean you are a regular everyday person struggling to make ends meet, if you live in one of London's poorest districts.
Similarly if you answer Barnes, Kew, Camden Town, Clapham, Hampstead, Highgate, Bayswater, Hammersmith, or Swiss Cottage you are likely to be in a very good job if not a millionaire. If you own a house in any of those districts you are going to be worth close to or more than £1m once the mortgage has been paid off.
