Easter egg: (Blu-ray) On Disk 1, open the "Extras" submenu and highlight "BD-Live". Press the Right arrow/button and a wire-frame of Iron Man will appear below it. Press the Enter button and a brief behind-the-scene vignette between Stan Lee and Robert Downey Jr. will appear.
Easter egg: In disk 1 under special features, right in between 'Preview' and 'Main Menu' a symbol appears when highlighted. Click and you can watch an interview with Stan Lee.
Answer: Tony, even wearing the Iron Man armour, is light enough that the shockwave of the blast throws him out of the way, so he escapes the majority of the explosion's effects. Stane, in his much heavier suit, isn't so lucky and so gets the full impact, which kills him. The flickering of the chest piece is merely a device to show that Tony is still in one piece, even if injured.
Tailkinker ★