First, I think that MGS4 will have some major impact on PS3 sales the coming month, but beyond that, very little. I simply cannot see people this autumn going "I need a PS3 because it had MGS4!". Much as I cannot see any game having that effect.
About MGS4 being a nisch game... Who said that being nisch or not had anything to do with sales? If a game appeals to the entire market it's a mainstream game, if it appeals to only a part of the market, it's a niche game, right? Has nothing to do with sales, imo. And that's all I'm going to say about that. I'm not in a position (and neither are most of you) to say which category it really belongs in.
I could see PS3 sales going up to about 450k tops release week, and going back to original levels (or thereabouts) within 4 weeks of release.
It'll be interesting to see how Nintendo moves. When GTAIV was released they pulled off a great stunt, and I wouldn't be surprised if they did that again, just to trump sony.
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