You don't have to spend money to wander in and out of stores and window shop on your way to other tourists attractions though. Unless you are in a rush that's kind of an organic thing in a walking city.
And if you have disposable income to use on Amazon.com while you are visiting NYC then presumably you could also spend a similar amount locally.
But you might have more money than you have time, in which case it makes sense to ship stuff from Amazon, and use the time you'd spend buying power adapters or extra socks or whatever to go and see the Math Museum or something.
And if you have disposable income to use on Amazon.com while you are visiting NYC then presumably you could also spend a similar amount locally.