Only somewhat valid reason I can think of is that Sony at first claimed motion controls to be gimmicky, and then did a quickturn and made their own controller. But even that should be seen as a victory for those Nintendo fans who embraced it from the beginning. Unless motion controls was only cool as long as it was exclusive to Nintendo.
Otherwise it's mostly the usual fanboy talk. "It belongs to us", similar to the recent FFvXIII discussions. You also have fanboys using the "Copy card", something you can also see with Sony fanboys trying to bash Natal.
I believe most Nintendo fans (the ones that liked motion controls, that is) are atleast a bit interested in both Move and Natal, but I also believe that many are disappointed, atleast in Move, when you look at the upcoming games. Most of the games have already been done on the Wii.
