Wii U sales trend may be just as expected if we look at Nintendo's home console sales.

[TheLegendaryWolf]

NES: 62 million       Atari 7800: 4 million        SMS:12 million

Genesis: 40 million          SNES: 49 million      AES: >1 million      TGx16: 10 million

N64: 33 million            PS1: 104 million               Saturn: 9.5 million

XB: 25 million      PS2: 158 million     GC: 22 million       DC: 11 million

XB360: 81 million    Wii: 101 million   PS3: 83  million

NWU: 6.1 million                                                   PS4: 7.2 million                                                             XB1: 4.4 million