MGS4 wasn't the only game to move hardware. GT5 definately boosted the PS3 hardware, especially in Europe and suprisingly, Uncharted 2 also gave a reasonable boost in console sales when it released.
I believe that God of War 3 may have boosted PS3 hardware as well but I can't remember clearly.
PS3 has system sellers, but they're so many diverse exclusives that no single game truly boosts the hardware by a huge amount like Halo or Zelda do.