Straights have changed markedly over the decades You will be hard pressed to find a Sheffield blade from before 1880 that WONT have a "smile" and yes, they were made that way

later razors that were actually the straight straight edges, there didnt seem to be as much need for an x stroke, but the reality is, most people did not have a 3in wide stone. hell, most people did not have a stone.
As for "why does it work" I'm pretty sure its because when steel comes in contact with an abrasive, metal is removed, and done properly can result in an edge being produced
I'm not even going to start on the bent razor problems