My logical explanation for this way of thinking is that in order to learn a language, you must practice.  Repetition of a word helps you memorize it.  As you play games (and I assume you enjoy playing games) and have fun, you listen to new words, hear pronunciation a lot, even repeat it as you discuss the game with friends.  So, for them playing games is a fun way of learning new vocabulary.

If it does work, what difference does it makes ?.  I once learned quite a bit of a new language myself by reading books, using the dictionary a lot and writing down translations (or meanings of new words) near or above word in question.  It worked for me, even if I do not recommend reading Don Quijote as a way to learn Spanish

It falls under the category of "learning through osmosis."  I mean that the only way I got through school was using my text books a pillows to give my brain time to asorb information.

So yeah if you want to learn via Half Life, you would get better results if you play it in a room of physicists. 

Because one of the number one factors when teaching is having fun. You also need to have some fun while you learn as well or else the lesson will be boring. I assume that they like to play games and think it is effective because they believe they are having fun while learning. IMHO playing games should come after the real teaching if you have time and it should be a game that is related to what you had already taught. Kind of like getting dessert after you eat your main course dinner. imo.

One of the highest reccomended teaching aids we learnt about at uni, when studying education to become a teacher, was games. They offer variety and interest to the learning process. People tend to remember things when they participate in it, rather than just listen to someone talk.

Even in uni, games are still entertaining and informative, though it might only be  crosswords or cloze puzzles to test learning, rather than plain old "question and answer" tests. And hangman is popular with all age groups, on occasions.

Lol! I am wondering what someone would sound like if they learned all their English from games like Counter Strike....

actually games are a great way to use english in practical scenarios. also games forces them to be creative in their thinking i love playing "sausage" with kids

Just for some context:

1) I teach adults. Most of my students are in their thirties.

2) I've been learning foreign languages for a good twenty five years now, and in my experience, the only way to do it is to bust your ass. Roughly, to be properly competent in a language, you need to be able to properly use 50,000 words on a daily basis, and you need to be able to understand about three times that. Plus far, far, far more idioms. Plus grammar, pronounciation and all that other good stuff.

It's one thing to bribe the little children with games to get them to do something they'll never be interested in. It's another thing entirely to waste time with people who should be mature enough to put in the effort they need.

The Francis and Kucera English Usage Analysis allows that the 2000 most common English words provide about 80% comprehension in formal English, and about 96% comprehension in natural English. It also allows that a  colllege graduate will have about 15,000 words vocabulary, providing 96% comprehension in formal English (roughly the same as 2000 words in natural English).

Games and role plays allow for an easy way to practice natural English, which is the English that students will encounter in the majority of interactions with English speakers. Formal English simply increases vocabulary without significantly increasing comprehension.

Just to clarify:

1) My numbers were taken from the various studies done by Seashore and Eckerson (rounded from memory).

2) My choice of wording was poor. That estimate is based on words that a native speaker uses, in general. You might not say a word like "flashlight" or "baggy" or "wheel" every day but, nevertheless, they are words that most native speakers are familiar with and would comfortably use should the situation arise. I go months at a time without saying the word "ambulance", for example, but it doesn't mean that it's marginal or obscure vocabulary.

3) S+E focuses particularly on high-status, well educated people. Most people who learn a foreign language want to sound mature, professional and well-educated. I forget that most 30- or 40-something Chinese want to sound like a teenager with a backwards baseball cap.

4) I don't disagree that  words like "the" or "and" are extremely useful, and make up a good percentage of our day-to-day usage, but words like that can only get you so far, if your goals are actually being able to operate with near-native proficiency. Go google up a Swadesh list, or a list of "simplified English" vocabulary, and ask yourself if you could hold a good job/rent an apartment/get a driver's licence/call a repairman, etc with just those words. 80% Chinese comprehension wasn't good enough for me when my (landlord) asked me to check my (gas) (meter), or I needed to (figure out) the new (tax) (laws), or when I needed a new (perscription) for my (nearsightedness) and I had to (judge) (varying) (levels) of (clarity) for the eye (exam).