Why did he throw his lightsabre away anyway?
I don't think he could have called his lightsabre to him, but I think he could have called his fathers lightsabre to him cause I think that on one of the barrels, when luke goes over to his father I swear that u could see vaders decapitated hand on one of those barrel thing's so that could mean that his fathers lightsabre was near.
Jolly and Overlord are right. Not only had Luke decided not to fight any more, for fear of falling to the Dark Side and for wanting to defeat Palpatine's mission to turn him, but how was Luke supposed to know that Sidious could cook his goose with his bare hands? It is not as if Yoda warned him to look out for the lightning. Even if he had, he wouldn't know how to defend himself, and seeing as he does not have Master Windu's strength, he would probably be thrown back anyways.
In the novel, he tries to divert it with the Force but fails, I must note.
Ok, if you were a Jedi, and a Sith just suddenly shot Sith lightning at you, would you have the reflexes to Force pull a lightsaber, catch it, and turn it on before the arc of lightning hit you? Mace could do it because he was holding it, Luke didn't even pay attention to where either of the sabers were dropped. So a better question is:
Could you think of blocking lightning with your saber, decide that you could, remember where the saber was dropped, turn over, Force pull it, catch it, ignite it, and block lightning before it hit you?
The 2 Jedi who deflected it both had their lightsabers drawn and ignited. And lets face it, i'm not a jedi but I reckon i could stand with a lightsaber in front of me and just let it soak up any lightning that any troublemaking sith who thought he was a bit of a hardman threw at me. It doesn't look too hard.