Well, not much in the way of an atmosphere exists at an altitude of one hundred miles. Any atmospheric conditions which might exist can easily be compensated for by computer controlled maneuvering.
Computer controlled maneuvering doesn't part the sea or make people walk on water. Its not a miracle. The only thing it can do is measure many times a second to see where power is needed. You still need the onboard computer (which can be small but not feather light), maneuvering jets of somekind and propellant that could overcome the high winds of that altitude that can point in any direction, a constant power source (the sun isn't always there, so you'd need heavy batteries), a material that can withstand the torsional stresses of being thrown around by the wind, and (lets face it) a miracle.
They can't. Only a small portion of the world can see a satellite at a time. The area of the world which can see the satellite depends of the satellite's altitude, of course.
As a rebuttal to your assertion that anyone in the Northern Hemisphere can see the same satellites; Can a person in New York see a satellite over China? Even in your own model this is impossible.
Sorry i forgot to mention the quarter hemishpere. Now lets ask your question again with a more realistic mindset: Can someone in Toronto see the same satelites as someone in Florida? Yeah, they can. And before you ask for proof, I've been ALL along the eastern states of the US, and I can tell you, my dad tracks the same satelites we see here quite well.
Btw, though I have not proved it as I've never been to china, they can see the same satelites at different times. I assume you chose China and Ney York since they surely can't see them at the same time? Seems like you're lashing out.