Yes, I play games that include advancement because I like advancing and life doesn't give me enough of it. That doesn't mean that my life sucks, it just means that life is more reasonable than games and can't fully provide me with what I want.
Excitement
Many gamers play for the sake of excitement, for that kick of adrenaline that they get from dangerous situations. Doing the same things in real life would no doubt let the adrenaline flow as well, but would be far too dangerous. This doesn't mean that gamers can't have excitement in real life, but games allow them to limit the personal risk (and risk for others) that is included in their need for excitement. If you're playing Left for Dead for the horror factor, you are using games as a substitute. Possibilities
I can't fly without the help of an aeroplane and usually I don't even get to steer those. (I have in the past, but not having a license somewhat disqualifies me there.) I can't shoot fireballs either and the number of princesses that need rescuing in this world is severely limited. There are quite simply a lot of things that I would like to do or experience but physically can't. With a certain willing suspension of disbelief, games and other media can give me access to those things. Notice a pattern here? I play games to provide me with experience I cannot or should not have in real life, and so do you most likely.
People
There are many people who have a lot of friends (and not only on facebook) but there are also people who don't have as many. Some people are born with physical disabilities, others are shy, live in a bad (or remote) place, or simply don't find common social activities very interesting. Enter multiplayer games in which you can be just as social as you want to be and have a huge pool of people to pick from. You even have a rough pre selection as you will find other players that like games in those games. Sure, there will be players who neglect a good social life for a game, which isn't a good thing, but there are far more players who complement their lacking social life with games. Gaming doesn't mean you can't go out and drink or dance but it does allow you to opt for an interesting (or fun) conversation instead if real life doesn't currently provide one for you. Pen pals have been commonly accepted for ages now, how is an online friend worse?
Competition
I'm not very much into sports. I go running somewhat regularly in order to keep my body in shape(ish), but I don't play competitive sports out of lack of interest. I like competition, however, and games can give me lots of that. Depending on what you like, you can compete based more on your twitch abilities or on using your brain instead. Real life sports mostly offer you to compete based on your physique while games can give you a wide range of fields to compete in - and players to compete against.
Immersion
Immersion is actually a part of the "possibilities" and "excitement" sections, but I put it here separately because of the way it is criticized - or not understood. Reading books and watching movies to be immersed in a story is perfectly fine from a social acceptance point of view. "I watched a movie and then snuggled into bed with a good book." is a valid answer to a question pertaining your evening activities, while "I played a computer game." often isn't. In both cases you are immersed into a fictional story - if it's a good game you might even be more immersed than in the other media. Yet somehow playing a game has negative connotations while reading a book has positive ones, even if both are used to escape from reality for a few hours.
Conclusion
There is nothing wrong about using computer games as a partial replacement for certain real life activities and desires. The problem only arises when a player doesn't know moderation, just like with other things in life. Doing one thing exclusively is rarely good - be it working, playing basketball, reading, or playing computer games. Each of these can be used as a substitute for others to a certain degree, however, without causing any problems. The next time you write about how we achievers only care about in-game success (e-peen!) because we don't have enough of that in real life, consider my answer to be "Yeah. So what?"
