1) Larger franchises than MGS have already launched on the PS3 to no avail. MGS4 will do the standard 280-400k that all the big PS3 games have done, maybe more because of the major effort to push bundles, but it won't hit the 800k that MGS games did on PS2, and it won't move millions of consoles.
2) "Monster Truck" is Wii exclusive on consoles (and not even a big hit on the consoles). They also don't love PSP games, at all. After the "Monster Truck" games, only four games have broken 300k; Crisis Core, Hot Shots Golf, Metal Gear Solid, and Final Fantasy Tactics. One of those has already fizzled on the PS3, one is about to launch, FFT is now a handheld franchise, and if there is going to be an FF7 remake I can't imagine it'll be coming any time soon, and certainly not soon enough to reverse a trend that's been locked down in solid steel since day one.
3) $200 isn't going to happen for many many years and the last major price drop for the PS3 had the effect of temporarily boosting sales for a month or two and then having them drop back lower than they were before. Maybe $200 will be enough to give a boost, but that's NEVER happened historically. Did the GameCube sell at $99?