From day one (with the XBox) Microsoft has been focused on capturing the American Core Gamer audience at the exclusion of all other demographics ... I presume that they expected that these influential gamers would (eventually) bring in the masses.
Most of the people who own XBox 360 systems see the game line-up with all the games they want, in all the genres they care about, and a few token games in other genres and proclaim that "The XBox 360 has the best and most diverse line-up!" The reality is, if that were the case everyone would see it and the XBox 360 would be selling like hotcakes.
At the same time it seems like the PS3 was designed to be in direct competition with the XBox 360 for this small demographic, and they seem to share most of the same games (which are virtually identical across platforms) so I can't see either system "losing" in comparison to the other based on their line-up diversity.
Now the Wii is another beast ... Designed to appeal to a very broad demograph it should have the most diverse line-up; so far we have only really seen this diversity comming from Nintendo, and in order for it to have the most diverse line-up third party publishers will have to step-up their efforts.
