I agree with TheCubedCanuck. Extras played a small roll--the fact the PS2 had a constant steam of must have games is what proprelled it, with GTA as the exclusive to solidify Sony's place.
This has been Nintendo's biggest weakness this gen. They have a stack of amazing games, but none of them generated that must have excitement that Mario 64 and Zelda: OoT had in the last generation. You can chalk that up to a combination of embarrasing promotions and the reality that these games just do not have the same appeal anymore. Nintendo doesn't have the kids market anymore, Sony has, so I think the best thing for them to do now is what they have begun doing in the last few months. They need to offer a broad range of titles rather than putting the burden on their usual suspects and assuming that the kids market is in their hands. I love their design philosophy, but truth be told this is no longer a family market.
A good illustration of this point is the Henry Hill thread that was posted awhile ago. While I feel Nintendo should be proud that can still design games that can appeal to wide range of people, even a harden criminal--the sad fact is Henry Hill does not buy games. His son buys games, and he clearily stated his feelings on how uncool Animal Crossing is. That one interview most clearly shows that battle Nintendo is fighting.
Nintendo doesn't have to be in first place, they have shown that in two generations. But I don't think it's good to be in 3rd either. I have been looking at 3rd party sales, and I have been confused as to how some titles still sell low even with a userbase that is supposedly bigger than Microsoft's. Part of it is fans that prefer Nintendo's offerings, but another than I don't see too many of us talking about that needs to be factored in is number of people that have the GC as a secondary system. I'm willing to be that a good part of that "40% are over 18" number that Nintendo presented at E3 are multi console users. Combine this with the fact that multi-platfrom titles usually get a weak treatment on the Cube, then you have the beginning of the blame cycle. I still think 3rd parties can sell on the Nintendo consoles, but you can only apply a multi-platform strategy in the rarest occasions. The problem is, people are buying Cubes for exclusives games while the rest of industry is moving towards an EA model for software sales. Exclusive titles are becoming an endangered species.
Nintendo can't stay in 3rd place if this is where the industry is headed. I think they realize this and now have a lot things going on behind the scenes for their next gen offering to insure that they are firmly in the 2nd spot rather than playing a who's who game with MS again. Iwata has recently made statments about finding new franchises, so I think they realize that Mario and Zelda will no longer carry them.