He crosses as he does, in my view, since that's the most effective method from the positions he usually finds himself in. The whipped cross favoured by Beckham and the like is, more often than not, done from deep and almost on the touchline. It needs pace on it or it'll be easy to defend, and it focuses on a general direction into the box for maximum effect, rather than picking out individuals. Valencia on the other hand is pacy as feck and will regularly beat his man and get to the touchline. Plus, more often than not, he's nearer the edge of the area than he is the rightside touchline. From there, it's far more possible to be hitting players, rather than just relying on putting it into dangerous areas and hoping someone gets on the end of it.
It's the beauty of Valencia really. Whilst Nani can perform all the tricks and beat a player from a running start with his pace, Valencia can go from a standing start from deep in the right wing, to the touchline, regularly. He doesn't rely on fooling a player with stepovers or whatever, he'll just do his "one trick pony" move of shifting it past the defender and using his huge acceleration to get on the end of it. That's pretty much half the work of the whipped type cross already, then he's at the touchline and able to pick someone out, on the floor or in the air. I like it a lot.