Gen 4? Even if I'm being generous and start with NES
NES ->SNES ->PS1 -> PS2 -> Wii/PS3/360
That's 5 already dude.
I guess now it starts with PS1, either due to the advent of 3D or the advent of Sony blowing the mainstream wide open. Either way I think it's really stupid to treat it as if the prior generations don't matter, it should either be from the very start, or at least from when the NES resuscitated consoles.
Alternatively, their view is more along the lines of this: the start of games period (Atari), the start of sophisticated 2D design (PC/Nintendo), the start of sophisticated 3D design (Sega/Sony/Nintendo/PC), and the start of serious alternative controls (DS/Wii/Move/Kinect/Wii U/next consoles... though I guess that should've ALREADY started.)
EDIT: Yeah, guess it's the former afterall. Maybe it's just from being raised on NES/SNES but I really don't like that kind of division, especially as A LOT of what was relevant then stayed relevant to more recent generations, nevermind where handhelds fit.