I don't see any upcoming game that is truly a system seller apart from maybe Zelda, Final Fantasy and Gears of Wars 2. (That is obviuosly not incluiding any casual game such as Wii Music or GH).

Actually... now I'm not sure about system sellers... Look at GTA... that used to be a system seller, not anymore. 

Games were system sellers generations past by bringing in core and non-traditional gamers. Hyped games on your HD consoles typically only get the people who've already been buying the console excited, or so I gather.

With GTA failing as a System seller, it does make you wonder.

 Either you are going to buy 4 PS3's, or none of these is a system seller for you.  It is libraries that sell games (as you illustrated here) with one game being the tipping point as others have pointed out.

I think MGS4 will see a HW boost similar to GTA4, and software will also follow a similar track.  Great sales, but not quite the second coming of Christ as some PS3 fans seem to expect.

 I also don't understand why is "system seller" are games from series he never played. If I never played a FF or MGS game before, I would go back and buy MGS 1-2-3, FF6-7-10-12 before playing the new ones.

 The point that MGS4 is included in with every 80gb PS3 sale is enough to give it legs.

Then perhaps the question should be, which is the better system seller? Wii sports or MGS4, lol.

 This is exactly what will happen. SONY fanboys be prepared for dissappointment. It's funny how GeOW sold more than 5mil with a smaller install base and now even diehard SONY fanboys prolly think it will only sell 4mill and largly thanks to it being bundled. I think SONY knew this would happen hence bundling it to keep it an exclusive and not make it look like a dissapointment. MGS4 is no way a system seller, its more of a niche product and the main reason there will be a HW boost is because of the new console. Atleast MS wasn't that desperate to bundle Halo 3 or GeOW cause they were confident and knew how to market their games. When's the SONY fanboys going to release if you keep believing in the hype SONY sells it will always lead to dissapointment. And also due to the speculation that it will come to the 360 sales will not even be close to what it was for Halo 3. And considering the fact that most ppl already own a PS3 want the game, its the slowest time of the year in sales and you have got  the equation for major disappointment.

The answer is Wii sports, but the question is pointless.

MGS4 will move a lot of hardware... emotionally... with Snake's 90 minute Oscar-worthy emo cutscenes discussing the futility of existence and war and blah blah blah.

There's no way it will move systems to anyone who wasn't considering getting a PS3 anyway.