I always thought the turtle/tortoise differentiation was by the way they walk. Where turtles hind legs/feet go out to the sides and push it forward, tortoises walk on straight hind legs much like an elephant. Don’t know if this is true or not, just my opinion.
It's sort like comparing apples and pineapple. They are made the same sorta but turtles have a much different diet for example. They come from different continents, have different living habits. Turtles are much more water oriented and frankly some have more personality than most tortoises. Somebody like Will, will come on and tell you the biological difference, I sure can't.....I have more turtles than tortoises, but I'm a diehard Sulcata fan. I have 2.
Oh and to answer your first question, most people are stupid.