Why are Xbox and Playstation lumped together in sales metrics, but not Nintendo?

[oniyide]

RJ_Sizzle said:

oniyide said:
Wii U was bombing pretty hard

Xbox One is trailing Playstation 4 more than 2 to 1. What's the criteria to be counted in the circle? It seems kind of arbitrary.

the fact that they still make Xbox1s and discoutinued the wii u says its not arbitrary.