I wanted to be sure I wasn't mistaken about this so I did a quick search for video game sales of recent popular multi-platform titles:
Madden NFL 08
- 2.39m (360)
- 2.14m (PS2)
- 0.84m (PS3)
- 0.67m (Wii)
FIFA 08
- 2.59m (PS2)
- 1.34m (PS3)
- 1.16m (360)
- 0.57m (Wii)
NBA Live 08
- 0.51m (PS2)
- 0.46m (360)
- 0.37m (PS3)
- 0.09m (Wii)
Pro Evolution Soccer 2008
- 3.09m (PS2)
- 1.48m (PS3)
- 0.99m (360)
- 0.45m (Wii)
Tony Hawk Proving Ground
- 0.42m (PS2)
- 0.33m (360)
- 0.23m (PS3)
- 0.13m (Wii)
The Simpsons Game
- 0.97m (PS2)
- 0.75m (360)
- 0.67m (Wii)
- 0.40m (PS3)
Guitar Hero III: Legends of Rock
- 3.89m (PS2)
- 2.90m (360)
- 2.54m (Wii)
- 1.23m (PS3)
Need for Speed: ProStreet
- 1.92m (PS2)
- 1.31m (360)
- 1.19m (PS3)
- 0.48m (Wii)
Just these games alone total close to 40 million copies sold, 40% of those were for the PS2 version, by far the most of any of the consoles... which isn't hard to understand when you consider how many PS2's are out there.
Combined the PS2 & PS3 sales account for nearly 60% of these sales. The sales of the 360 versions accounted for about 25%, and the Wii only about 15%.
Based on these and other figures, I don't see Sony and game developers ending their support for the PS2 any time soon... at least not for another couple years.