Gran Turismo and Final Fantasy are system sellers, can't say the same about MGS, but sales of MGS are better in the U.S., so who knows. Maybe MGS 4 will drive console sales here in the U.S.
Then you look at the 360, and the only one that looks the most definitive of having associated with moving hardware is Halo, and to a lesser extent Forza. Bioshock may pull sales, but I don't know if it will indeed boost sales since it is also headed to the PC. Splinter Cell hasn't been associated with moving hardware and I think the same will apply to the new one. I think it will sell good, but not move hardware.
Dead or Alive and Ninja Gaiden have huge, huge, huge question marks over their heads as to being an exclusive on a specific console. Afterall, Itagaki claimed that he only wants to make games for the most powerful console, and here we are with Ninja Gaiden coming to the PS3, and for some odd reason, the DS is getting a NG game. Hmm.