Some of these PS4 sales predictions are astonishingly low

[ICStats]

Mitch2129 said:
All signs point to a shorter Generation though, I'd say around 85m if it's a 5 year Gen like i'm expecting, if it ends up being as long as last gen then, id say about 110-115million

Even if it's a 5 year generation it doesn't mean sales won't keep going as they did for PS1 & PS2.  Almost half of PS2's lifetime shipments were after PS3 released.

PS4 is ~10 Million units ahead of PS2 at the same point in time.  It's not too crazy to expect it to hit 100 Million within 5 years, and then keep going.

PlayStation 2 sales figures (production shipments) (based on official financial reports[1][2])
Date	Total sales (cumulative)
Fiscal year ending March 31, 2000	1.41	1.41
Fiscal year ending March 31, 2001	9.20	10.61
Fiscal year ending March 31, 2002	18.07	28.68
Fiscal year ending March 31, 2003	22.52	51.20
Fiscal year ending March 31, 2004	20.10	71.30
Fiscal year ending March 31, 2005	16.17	87.47
Fiscal year ending March 31, 2006	16.22	103.69
Fiscal year ending March 31, 2007	14.20	117.89
Fiscal year ending March 31, 2008	13.70	131.6
Fiscal year ending March 31, 2009	7.90	139.5
Fiscal year ending March 31, 2010	7.30	146.8
Fiscal year ending March 31, 2011	6.40	153.2