I've seen figures which suggest PS1 did anything from 35m - 40m in the Americas. Wii is going to pass it rather easily here. These are the estimates / figures I've been able to cobble together for the USA market.
Wii: 2006-2010 (USA) - 34m-35m
DS: 2004-2008 (USA) - 27.5m
PS2 2000-2004 (USA) - 26.7m
NES: 1985-1989 (USA) - 20.7m (huge peak in 1989 seperated it from SNES)
PS1: 1995-1999 (USA) - 20.6m (very similar trajectory to NES actually)
SNES: 1991-1995 (USA) - 20.0m
X360: 2005-2009 (USA) - 18.7m
PSP: 2005-2009 (USA) - 16.9m
N64: 1996-2000 (USA) - 16.7m
PS3: 2006-2010 (USA) - 15m-15.5m
Xbox: 2001-2005 (USA) - 14.0m
GC: 2001-2005 (USA) - 10.7m
Genesis: 1989-1993 (USA) - 10.2m
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu
