Trivia: The photo of Cap in Tony's tower has the number #25 - the issue number of the comics in which Captain America dies.
Trivia: When Thor and Hulk battle on the helicarrier, Thor hits Hulk, who collides with a Harrier jump jet. The prop Harrier which Hulk hits is the very same one that Arnold Schwarzenegger flew in True Lies.
Trivia: The first movie to ever gross over $200 million domestically in its opening weekend. (And somewhat coincidentally, it was released almost exactly ten years to the day after "Spider-Man" - the first movie to gross over $100 million in its opening weekend, and also based on a Marvel property).
Answer: While Loki is not immortal, he's just as powerful as Thor, and many mortals would consider him a God as well. Loki is actually a Frost Giant taken in by Odin, but is just as invulnerable to many attacks. There may also be an element of magic involved in his survival as well.
Bishop73