These two stories serve to show what other characters were up to while Wolverine was uncovering the events of House of M. They provide backstory into why certain things happened towards the end of the series.
In the Fantastic Four arc, Reed Richards and Susan Storm died when they went up into space. The radiation from the cosmic cloud was too much for them to handle. Instead of Johnny Storm, J. Jonah Jameson's son John accompanied them and also ended up dead. Ben Grimm was there as well, and barely made it out alive. The shuttle crashed in Latveria, home of Victor von Doom. Doom, who never suffered an accident (thus he needs no mask) is the King of Latveria, and things seem to be going well for him. His mother is alive, he has a great family, and, even though he's human, he is Magneto's second-in-command. However, he desires more, but since he is human, this is as far as he will ever get. Until he is inspired by the corpses of Richards, Storm, and Jameson. He realizes that he can develop a method to safely harness the radiation that mutated the Americans to give his family superpowers that parallel those of the Fantastic Four. Using Ben Grimm as "The It", his wife as the Invincible Woman, and his son as the Inhuman Torch, they try to usurp power from the House of M.
The one thing I found kind of strange about this story is that the point of House of M is that the Scarlet Witch gave the people she knew their greatest wishes. However, since she was an Avenger, it is more likely that she knew Reed Richards and the Fantastic Four and would have given them their greatest wishes. Other than that, this is an interesting look at Dr. Doom and how he would have preferred his life to turn out.
In the Iron Man story, Tony Stark is still billionaire industrialist, but now he works out of Chicago. He is pretty much the most respected human in the business world, and he is famous for his skills at "Sapien Death Match", an American Gladiators-type show in which he, Johnny Storm, and his father (who is alive in the House of M reality) don power suits to fight sentinels. While on the surface Stark seems to be ok with the mutant domination of the world (most of his technology that he develops gets sold to the House of M to use against humans), he keeps his greatest invention to himself in order to use to help the oppressed humans. Hank Pym has a pivotal role in this story, and the introduction of his character in the main House of M arc pays off here.
Of the two stories, I preferred the Iron Man one. They both have their merits, and they both effectively enhance the main House of M storyline, so this is definitely more for comic purists and completists.