Wired's Chris Baker has a piece up over at Slate detailing why the PS2 still is on top...

"Luckily for Sony, their old console is so popular—more than 100 million have been sold worldwide—that they can offset some of the money they're hemorrhaging with the PS3. By continuing to manufacture and support the PS2, Sony is keeping its old customers happy and offering a cheaper alternative for people who can't afford a next-generation machine. Sony did the same thing last time around and managed to sell more than 20 million of the original PS1 consoles between 2000 and 2004—after the appearance of the PlayStation 2."