Clipping / Easily Cancelled Auto Attacks due to long wind up (Karthus, maybe more)

When you attempt to auto attack with karthus, it is easy to cause it to clip and cancel the auto attack, because the wind up in the animation before the attack is released is very long. This is not very helpful, and I don't see why it wouldn't instantly launch an attack like many other champions. What is the reason for the wind-up? It makes it very hard to last hit with the auto attack of karthus...

Even if you have to change the animation to a spear like poke or something, this would be far better than the 0.5 second swing he does. If you move while he is swinging this cancels the attack and he does not release the projectile...