Question: One of the early posters of this film shows a bearded guy (who is not in the film) coming through a wall crack and holding puppet strings with one hand. Who is this guy supposed to be and what does he represent?
Answer: It is Stephen King.
Question: Why is it that the machines they used to fight back didn't try to attack the humans? The military vehicle had a .50 cal machine gun that shot AT them, but their guns seemed to work just fine.
Answer: It should be noted, the ending title cards seems to set it up so there are no plot holes and answers any "why" questions (which, intentional or not by King, can be debated). While the opening premise is the comet's close pass by Earth caused all machines to turn on people, at the end, the Russians blew up a UFO 2 days later, suggesting that it was the aliens controlling the machines. Bill suggests aliens are trying to wipe out humanity (although at that point he's just guessing and had no evidence of an alien or UFO present), but it can be debated the actual premise was that aliens were just testing or experimenting on people.
Answer: The movie is infamous for its plot holes, among them this one, and "How come cars didn't start attacking people"? From the story point of view we can surmise that the M60 is part of the vehicle's structure, while hand-held weaponry stay inert.
Question: How and why does the glass on the pinball machine shatter all by itself?
Answer: The Pinball Machine overloaded at speed.
Chosen answer: He does bear a striking resemblance to Stephen King. King was both the writer and director of this movie, and as such, was certainly the guy in charge of all the character's fates and pulling all the strings.
Twotall