Lex Luthor: Gods are selfish beings who fly around in little red capes and don't share their power with mankind.
Lex Luthor: C'mon, let me hear you say it. Just once. C'mon.
Lois Lane: You're insane.
Lex Luthor: No! Not that! The other thing. C'mon.
Lois Lane: Superman will never-
Lex Luthor: WRONG!
Superman: Your wrote that the world doesn't need a saviour. But every day I hear people calling out for one.
Lois Lane: How did you get here?
Richard White: I flew.
Lex Luthor: Kitty, what did my father always say?
Kitty: You're losing your hair?
Lex Luthor: Before that.
Kitty: Get out?
Kitty: Wow. That's really something Lex.
Lex Luthor: Wait for it.
Kitty: Wow, that's really something Lex. It's freaking Gone with the Wind.
Answer: There are two stories: a) the suit was made by Martha Kent from the blankets which came with Superman when he was a child and these blankets got superstrenght from the sun too. b) Superman generates an aura which protects him and his suit against such forces. Both stories can be true: either the suit itself is weakend by the kryptonite or Superman's aura was weakend by it. Currently it is said that the blanket-story is the correct one. Also, they don't actually cut it off him - it appears to open along a predefined line (coupled with someone exclaiming "got it!"), presumably the method Superman uses to get into the suit himself.
Bjoern_Buller