Easter egg: Second easter egg on the Region 1 two-disc Special Edition: On the first disc, go to Languages. Place the cursor on "Francais" and press Up once. A red Superman logo will appear next to Brandon Routh's right fist. Place the cursor on this logo and press Enter to access a special cheat code for the "Superman Returns: The Game" video game. Not a traditional easter egg, but an easter egg nonetheless.
Easter egg: Easter Egg on the 2-disc Special Edition Region 1 DVD: Go to Special Features, then Deleted Scenes. Place the cursor on "Features" at the bottom and then press Down once. A red Superman logo will appear below "Features" and "Menu." Now select the red logo and press Enter and you will see some funny outtakes of Kevin Spacey doing his "Wrong." scene.
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