Because I lived in NYC and rode the subway multiple times every day all over the place and this is what I experienced. Lots of data points collected that were all consistent. Of course you don't have to believe me. I provided a couple short examples that demonstrated what I was talking about. I've seen plenty of other things but they are more difficult to explain. If you have routinely used the NYC subway and had a different experience please share, otherwise just take it as the impression from a fellow HNer.