Not a difficult prediction to make. No one's actually expecting the Xbone to reach Xbox 360 sales, 360 is the best supported MS platform ever and it barely made it past the PSP. Xbox is losing the market share it captured from PS last gen. Nintendos hardware business is dwindling, the 3DS has peaked, mobiles changed the handheld industry forever, the next Nintendo handheld will likely have trouble reaching even the 3DS sales. Same story with their home consoles. Nintendo consoles sold less each gen since the NES if the Wii is left out.
NES: ~61M
SNES: ~49M
N64: ~34M
GCN: ~22M
WiiU: ~16M?