I want to know what a grandmaster does to earn a living, because if he has a 2600 rating then he is not able to win many tournaments.
Adding to Rickka's answer: Coaching, books, articles/reviews/analysis for chess magazines/web sites, commentary, participation in smaller tournaments (both for the prize money and appearance fee) and simuls are common avenues of income for GM's.
Acting as a second for a super GM is also quite common. Super GM's can afford to "outsource" some brunt work like studying opponent openings/styles and providing a practice board for novel ideas.
Some 2600+ GM's also have normal non-chess related jobs. Matthew Sadler works in IT, for example, and considers chess as a hobby. I also saw a brief inset on a woman IM (unfortunately I can't remember her name now) who works in marketing for a company that likes the prestige of being associated with chess.
I just want to add that in many countries, chess is considered as a sport and those grandmasters are paid by the government. For example, the top Chinese players receives stable income from the government. The money they receive is definitely not impressive, but it's better than nothing. Not every country does that, at least as know the US doesn't believe a chess player should be paid by the taxpayers' money.
2500- and 2600-rated grandmasters win tournaments every year. They're just not the high-profile events like Wijk wan Zee or the like. For example, The top three at the recent British Championship were all under 2700, 2 under 2600. Also the French championships.
Run through the events listed in theweekinchess.com sometime...you might be surprised at how many tournaments are won by players under 2700.