Maskedbishop - even though you started this debate, it doesn't seem like you care much about anyone else's opinion on this topic since you seem rather content with just telling everyone that studying GM games don't help. Most people who study GM games aren't studying it properly or just browse through it like they would a brochure so they obviously won't get the benefit from it.
Studying GM games is probably one of the most important things a chess player can do because of the many reasons already presented here. I don't see a lot of point arguing with here on a chess forum so I'll just say this - most people are awful at chess, whether it's because they're old, not talented, not hard-working enough, not given enough opportunities, introduced to the game too late or a variety of reasons. Trying to extrapolate from a series of terrible absolutes (authors only use GM games, chesslife only uses GM games, everyone must study GM games) and using that as the crux of your "statistics" is not something you should strive for when trying to convince the masses of your statement.
Yeah, well, you see these books recommended all the time. Some of them have been on the shortlists for decades. I'm not convinced they are adding rating points.
You read something like Understanding Chess Move by Move and it's yeah, great, nice move GM...and thanks for telling me why they did that, Mr. Nunn.
But it doesn't make YOU a better player. You can watch golf and see Tiger Wood takes his 5 iron out, and have the reasoning behind that carefully explained to you. Doesn't mean if you are at the same place on the same course that your five iron is going to help AT ALL.
There seems to be an assumption that if you stare at their play enough, and have someone "explain" it to you, eventually osmosis will kick in and your own much more limited set of chess skills will absorb theirs.
I say...NO. That doesn't happen. Studying GM games will not make you a better chess player. It will make you a better chess enthusiast, fan, or reader. But your OTB skills will not significantly improve...because you will never think like they think.
You can learn to play piano, but it doesn't matter how often you listen to Horowitz, or watch his fingers move...you will never play it at his level.
You want to hear something funny? You know what it took for my rating to take off, and for my game to really improve?
Those Igor Smirnov courses...no kidding. He doesnt supply "magic in a bottle" Waht he delivers in his courses is nothing earth shattering or new. Its how he explains things.