Exactly. Even Yoda was knocked back from the blast of Sidious' Force Lightning. Granted the Lightning coursing through Vader wasn't the most powerful Lightning he could summon, but it was enough to torture Luke Skywalker. Had Vader been weak to Lightning, it would have no doubt killed him. He was already weakened from the duel with Luke Skywalker, the Lightning would have killed him had he been weak to it.
Hm? Wasn't it stated, that Sidious amped up his force lighting to full power? Or that he turned up the intesity when he was picked up.
"Now young Skywalker...you will die."
*Zap, zap, zap*
Then he gets picked up while still blasting the full force of his lighting.