Simple answer - HD gamers combine the two HD systems together so that they can find a way to say that they are winning against Nintendo.
The longer answer is - the oldest gaming rivalry was between Nintendo and Sega. When Sega stopped making HW, the tide went in favor of Sony, or the new Microsoft venture, the Xbox. These ex-Sega fans hated Nintendo so much for "destroying" Sega, (sega killed themselves, fyi). They began to recruit other gamers to hate Nintendo. This brought about the era of "kiddie" labeling of everything Nintendo, because apparently "mature gamers" played PS2 and later, Xbox (and only Xbox was given a pass because it had Halo). Everything about Nintendo had to be spat upon, looked down upon and laughed at. "Fisher Price" controller of the GameCube, "Waggle" and "fad" of the Wii.
When the Wii received its success, these angry people had to find a way to knock it down a few pegs, and they figured that if PS3 and 360 fans joined forces, they can say that together they outsold the Wii.
Ok, the real truth now - because most of the game libraries are similar/multiplat and the devs can double the amount of fanbase where Wii exclusives are .. well, exclusive to the Wii.
But admit it, the story of fanboy origins is a lot more interesting. 







