Pollutants like sulfuric and nitric acids from today's industrial processes and automotive exhaust become trapped in the raindrops or Snow flakes (acid rain) that settle on your vehicles surface. The sun will evaporate the water and leave the concentrated acids that can actually etch the finish of your car.
"Spot Free" water is generated by reverse osmosis to remove the minerals that create water spots when water evaporates. This final rinse leaves a "Spot Free" finish when residual water dries from your vehicle.
No. The wax itself won't streak the outside windows. However, grease and oil from road spray can coat your wiper blades which can cause the rainbow like streaks you may see. Wiper blades should be changed annually and cleaned regularly with rubbing alcohol and a cloth between changes to remove road oils.