Comic book collecting is the result of an interest in antiquity, and nostalgia, as is all collecting by it's very nature. The comic book was brought into the pop culture arena by,most notibly, Superman. Since the introduction of Superman there was been a surge in comic characters, books and companies entering into the industry. The industry is dominated by top competitors Marvel Comics (makers of such comics as Spider-Man, X-Men, Thor, Fantastic Four, The Avengers, and The Hulk) and Detective Comics (makers of Superman, Green Lantern, Wonder Woman, Flash, Batman and Sandman).
Since comic books tend to be like tv dramas; having a flowing and continual plotline with dynamic characters, many people, mostly a younger audience; from grade school students through college kids,follow their periodic- usually monthly (but weekly for big-name characters)- exploits. This leads to the keeping of these books, and after so long those who did not keep these books from their childhood want them back, why that is no psychologist can wholly agree upon, but nonetheless they want the things of their childhood back and are willing to pay.
That is how it started, but now it has boomed into the companies themselves releasing alternative versions of popular books, limited-editions, and other gimmicks to entice more buyers. Some collectors may buy five copies of the same story content, just because the book has a diffrent cover. They do this in the belief that the product will be in demand, and they can resell for a profit. With the coming of the 'internt-age' there has been a big interest in comic books,or at least an increased level of contact between collectors; sellers and buyers. Online auction sites, like eBay and Amazon.com are benifiting from this increased interest.
Comic book collecting is like all other collecting; some collect for-profit, others for memories, but all are drawn to the vivid colors, bright illistrations, and colorful characters of the comic book universe.