It seems that many of you forgot that PS2 sold multi-million units late on its life cycle in developing countries because of PIRACY. In the Philippines, you could buy a brand new PS2 console for $125-$150 and a pirated DVD copy of PS2 games at only 50 pesos ($1). Cheap price of games made PS2 a blockbuster console in Southeast Asia. But nowadays, you can not find pirated copies of PS4 games. A minimum wage worker here only earns 12,000 pesos (about $240) a month. So ordinary Filipinos who previously could afford to buy PS2 find the PS4 luxurious. Thus, only the people who belong to higher socio-economic class can afford to buy a PS4. With that, PS4 can never reach PS2's numbers.
As the article pointed out, the only chance the PS4 has of outselling or even coming close to the PS2 is with a price drop from $299 to $199 this holiday season and more price drops and deals after that. Basically everything needs to go right for there to be any chance, while the PS5 launch is as bad as the PS4.