You'd be hard pressed these days to find a popular item that hasn't had its brand expanded with a bunch of new products for consumers to snatch up. Games certainly follow this trend; for example, games that were originally planned as standalone works might suddenly spawn sequels if sales are higher than expected.
Then there is merchandise. If you fall in love with a game's world or its characters, you might feel tempted to buy figurines, posters and the like to demonstrate your fandom. To see the kind of items that are out there, just look to Square Enix, one of the biggest providers of game merch (due to Final Fantasy and Dragon Quest in particular). That little slime is so darn cute.
So, if you're an obsessive collector, now's your chance to brag about it. Do you have any MMO merchandise you're particularly proud of? Got a famous MMO mascot figurine on your desk keeping you company this very moment? How about non-MMO game merch? Or would you never, under any circumstance, pay for this stuff?