I think the demographics enjoying video games are seen as more homogeneous than they really are. Music and books aren't all marketed to the same people, but in general I feel that the biggest variety of acknowledged gaming demographics that exists is between age groups. And even then ESBR ratings are overlooked pretty heavily, leading to the "why are video games so violent? you know kids are playing them!" crap.
There's also the "casual" and "hardcore" demographic distinction, but from the abysmal reception of most of the titles designed for "casual gamers" and frustration with games sacrificing complexity for accessibility, I think it's safe to say that casual gamers are people who don't much care for video games. The only successful marketing toward casual gamers that I know of is the Wii.
It's no longer fair to draw the line at PC or console either. But there are real video game demographic disparities.
There's an entire approach to games that I like to call "sport-gaming". Yes sports games are often included in this, but I'm not referring to simulated sporting events. I'm referring games who's primary draw is competition with other people. It seems to me that this is use of the gaming medium that differs fundamentally from games which are designed to be immersive or tell a story. All games try to be fun, but sport-games rely on the fun of competing with other people.
Here's the distinction: sport-gaming is not about immersion, story telling, exploration, or information. The game is actually a little incidental. Despite graphics being present, you aren't playing a soldier and you aren't fighting an alien. You are you, and they are them. The actual people. You don't die or destroy, you lose or win. Rather than being judged based on a narrative or complexity or originality, sport-games are judged based on how they allow you to interact with others. I sometimes see Halo matches as basically touch football. The game is just a way for you to play a sport against someone
Experiencing a game as a sport makes the game a conduit between you and others. There is still a lot of focus on the game, but once you become familiarized with it, the game itself becomes almost invisible and the activity becomes much more about outsmarting and outperforming others. I think this is in fact why there's so much trash talk among people playing online games. It's not the same as playing against your friends. When not face to face, the desire to "better" becomes heightened, as does the need to create more tangible social contact.
There is a demographic of gamers who primarily play sport-games. Many games try to appeal to both types of gaming, narrative and sport. Often times this works perfectly well. I really like playing Starcraft's story. I have no interest in Gears of War online. There are a lot of gamers out there who seem to exclusively play games as sport, like game jocks. I seem to remember Gears of War not truly being accepted by 1up and IGN until it had sufficient multilayer maps and modes. Starcraft practically is an organized sport in Korea.
Part of this divide I think has to do with when you started getting invested in games. For those of us who grew up with an NES, I think there's more of a tendency to see video games as not really "games". Indeed this is where I see their value, as interactive narratives. While our parents asked "what's the point of this game" and were confused when we had a difficult time answering, we understood why our friends spent hours on games with "no real point".
On the other hand, there's an entire generation of gamers who only really began investing time in games during the X-Box era of online gaming. The growth of video games as a profitable industry I think is indebted to this type of gamer. Men young and old have video games, and many of them have no interest in fantasy narratives of any kind. They watch action movies for the explosions, watch sports to bet, and play games as sport. They pay for online subscriptions and they buy lots of titles.
Most of us participate in both worlds, but there are some who almost exclusively play online, and those who avoid online games like we avoid Hollywood clubs. It may be coming through that I don't particularly care for this type of gaming. I think it's like playing real life sports without any of the physical fun of playing real life sports. I'm trying very hard not to be snobby. But as much as I can admit that this is a useful way for people to interact, and a valuable way that video games have become embedded in culture, I do think that it's stifling gaming from being the expressive medium I think it should be.
Sport-gaming has to be repetitive. Rules have to be second nature, resources have to be familiar. The point is how you use the established game elements against others. If maps weren't small enough to memorize, controls simple enough to be predictable, and gameplay repeated enough to be accessible by players of different experience, the game wouldn't work. Playing the actual game can't be difficult or complicated, or the addition of unpredictable opponents would make the experience unbearable.
Video games are like comics in that they are just lucrative enough for them to be mass-marketed, but niche enough for the marketers to not know almost anything about the breadth of people they're marketing to. I don't think we as game consumers really know where we fall in game culture sometimes either. Maybe it's bad to draw lines in the sand and "other" different types of gamers, but I think some discussion of different types of gamers would be valuable.