More queries

I am puzzled by the formulations using "you need to" rather than what would have once been usual -- "you must" or "you have to" or a simple imperative. As in "You need to step away from the car, sir." This is not exactly accurate, is it? Do I actually need to? If it's short for "You need to step away form the car in order to avoid being Tasered" -- I guess that makes sense. But what need of mine is actually being pointed out to me?

And when did this start? When did it become universal? A...