Is there a logical reason why Jax's W can be cancelled while Nasus' Q (and others) can't?

... wut? can it? I've never heard of this. What do you mean by cancelled exactly. Irelia cant cancel hers either.. Actually what are you talking about lol

With Nasus, if you right-click a minion with Q active, you will perform the attack pretty much no matter what. While with Jax, if you right-click a minion with W active, if you move away you won't perform the attack (attack move). It makes trades much smoother because you can simply back off after using your empowered auto which in many case wins the trade.