The Wii hate is just an extension of the "Nintendo Hate" that has been evident in a lot of game journalism and game analysis since before the Gamecube launched ...
When I first started to notice the "hate" it was an obvious double standard when it came to the kinds of content Nintendo was delivering to their systems ... When Nintendo would release a Mario, Zelda, Banjo Kazooie, Donkey Kong, Star Fox (or other classic series that has a lot of demand) critics would always discount the games because (while they were great games) they were obviously made for young childrent; this criticism never found its way into reviews for Crash Bandicoot, Spyro, Sonic the Hedgehog, Dark Cloud, or (pretty much) any other similar game made by any other company. At the same time, Nintendo never received any kudos when they published games like Perfect Dark, Golden Eye, Eternal Darkness (or any other game that couldn't be classified as being "Kiddie").
After Sega was forced into being a third party publisher, the main "Hate" argument changed from Nintendo being kiddie to Nintendo is doomed ... The Gamecube's cancelation was always around the corner and Nintendo was going to start developing games for Sony and Microsoft's consoles. The Nintendo DS was never considered to have a chance to beat the "Superior" PSP, and even as its sales took off the DS's decline (and the PSP's rise) was always just around the corner. This has continued into the Wii's generation but we're already seeing a fairly major shift in the argument again ...
Since you can't (exactly) argue that the market leader, who has several years of operating expenses in cash, is doomed the argument has changed to "Nintendo isn't for real gamers" and "Nintendo is killing videogames" ...