March NPD ended April 4 so the PS2 Q1 2009 figures do include about 4 days at the $100 pricepoint.
PS3 should be down through at least May given that Sony won't cut price before E3 if they do cut price in the first half of 2009. PSP should be down too. PS2 sold much lower amounts in April-June 2008 so it won't be down nearly as much in the second quarter, in fact Q2 it may actually be up on the price drop so citing a "sudden drop" seems like cherry picking to me.
The way things are going now I think we're trending toward this in the USA:
2008 to 2009 Trend Q1 Q2 Q3 Q4
Wii Up Down Up Up
X360 Up Up Up Down
PS3 Down Down Up Up
DS Up Up Up Up
PSP Down Down Down Up
PS2 Down Up Down Down
In July, when NPD data for the first half comes out I imagine we'll see alot of alarmist things about the videogame industry because PS2, PSP, PS3 will all be down probably 33%, 27%, 15% (with a June price cut) respectively, with Wii up only 10%, and 360 and DS will be up maybe 30% and 60% respectively. It should even out to 'only' 10% growth in the number of hardware units sold for the first half. But I figure with Motion Plus, a PS3 price cut at E3, and a new PSP model in October or November Wii, 360, DS will be up for the year, PS3 will be flat, and only PS2 and PSP will be down, with the former the only platform significantly down.
So if 2008 was
Wii - 10.16m
DS - 9.95m
360 - 4.74m
PSP - 3.83m
PS3 - 3.54m
PS2 - 2.50m
2009 should be
Wii - 12.5m-13.5m
DS - 12m-14m
360 - 5.25m-6m
PS3 - 3.4m-4.2m
PSP - 3.2m-3.8m
PS2 - 1.6m-2.2m