Actually, I think this is brought up every fews pages or so. It wasn't just the lightning, it was also his use of the dark side that "deformed" him. Luke wasn't shooting out intense Force energy and then getting it sent back to him. While we have examples of others getting hit by lightning, Sidious is the only example we have of anyone being struck by their own lightning while at the same time shooting out more lightning. Keeping in mind that this is as theoretical as just about anything else in this thread.