It's current theory in football, probably stems from Messi and Arjen Robben ,both left footers who are actually better down the right than they are down the left.As to why you'd have to ask a sports scientist, it's something to do with turning in when the defender expects you to turn out. Also the angle of the resulting cross has something to do with it.
However what may be true for Messi,Robben and Van Persie is not necessarily applicable to BWP and Smith.