Somebody at GAF pointed at this:
US Nintendo consoles launch
NES - late 1985
SNES - 8/23/1991
N64 - 9/29/1996
GCN - 11/18/2001
Wii - 11/19/2006
So yep the famous "5 year cycle" is quite real in NA; in Japan the first Famicom was released in late 1983 and the SFamicom late 1990 (that's the only Nintendo console with a different cycle; 7 years), so anyway, will Nintendo continue with the idea of releasing the next console late this year (that'll explain the early release of the 3DS) or it's going to release it next year making the Wii the second console with a loger life cycle in the company??