oh that combination works wonders on multiplayer fps (ala Quake 2) yes its awkward at first, but once u get the hang of it theres no going back to up, down, left, right, ctrl, shift!

its simply a matter of faster and higher accuracy when shooting with the mouse!

I think the only reason why people used to play with arrows was the picture of arrow in those. But if there would be for example numbers on those keys, probably no one would have used those.