Remember that transiting traffic is not cognizant of the heliport locations or their landing / takeoff patterns. Yes, one could put them on the map but do you prefer transiting pilots with their eyes outside or on the map?
If you are transiting in the Hudson, you should be very aware of where the heliports are. If you were transiting any other area with so many aerodromes in such a concentrated area anywhere else, you would make yourself aware of the direction of runways in a bid to figure out where the local traffic is most likely to be. Or at least you should.
Take the Flying W(N14) area of New Jersey, for example. 3 uncontrolled airports within a 3 mile radius. I wouldn't dream of transiting that area at pattern altitude without a good mental picture of where the local traffic would be operating.