I think many people don't like seeing a medium size company competing againt giant corporations like Sony and Microsoft, they see Nintendo as a relique from another time, and wish the videogame industry were all about huge corporations pushing and competing with the latest most advance technology.
After Nintendo 64 and the Gamecube they thought Nintendo was soon going the way of Sega, and they were extremely bothered by Nintendo outselling Sony and Microsoft last gen, they didn't expect that at all. As if Nintendo, the toy company, were not allowed to be more successful than the HD twins, as if it was something outrageous.
I think the hatred some people feel for Nintendo comes from that, and after the Wii sucess the hatred was made stronger because they realized Nintendo was not that harmless and could be quite threatening if they got lucky.
That is why they get all excited and wet when they think of Nintendo going third party.