As someone who mains Veigar I appreciate that. Late game it gets hard NOT to KS since my lowest spell does 800. Although I actively try to provide the assist with Event Horizon. The other thing I do is the EH + Dark Matter combo (effectively saying: you weren't doing it fast enough, you have 1.2 seconds to kill them before I do).
Favorite moment: I was heading to kill someone squishy, teammate notices and starts out about 2-3 seconds behind me. He didn't even get the assist.
But a nuke or a nuke combo like Veigar's isn't KS-ing. =D
Neither is a Shen Ultimate to save your ass and end up with the kill. Sure you did 70% damage but you would be dead without him. =P