People finding cabs on 5th avenue at 6pm know there are no cabs to be had. You can't just raise your hand. It could take 15 to 20 minutes to find a cab.
So suggesting that you can get a cab 90% in NYC is a statement of fact, but it's not actually true.
Facts: http://www.schallerconsult.com/taxi/taxifb.pdf
That's one of the many reasons Uber is also crushing it in NYC.