Sony may have you believing that the company cut out PS2 backwards compatibility in order to save costs, but the real reason is actually more strategic than anything else. All PS3s will most likely be able to play PS2 games in the near future.
The PS2 is Sony Computer Entertainment’s crowing achievement after the PSOne. Both consoles combined have sold close to 260 million units world wide. It does make it seem a bit silly when you see console fanboys bickering over the anthill-sized 20-some -million units for the PS3 and Xbox 360.
The PS2 and PSOne has a combined library of over 8,000 games (PAL, NTSC) to date, yet the latest version of the PS3 cannot play any of the PS2 games. I was fortunate enough to get my 60GB PS3 during launch, which is considered by many to be the ultimate version. I consider it to be the MVP (Most Valued Player) of gaming consoles due to the fact I could fence it for a good bit of cash on Ebay.
The 80GB, which came out after the 60GB, had a new piece of software minus the Emotion Engine (PS2 processor) and could play PS2 games. The emulator actually works quite well with support for 85 to 95 percent of the PS2 games out there. However, the latest iterations of the PS3 cannot play PS2 games at all. The system can still play PSOne games but will fail to read PS2 discs.
The main reason why Sony took BC out of the PS3 is because the PS2 is still selling well. Believe it or not, according to NPD the PS2 managed to sell about 1 million units during the four months within the holiday season. These figures are for US only.
Also, out of all the production consoles out there right now, the PS2 also brings in the most profit per manufacturing cost. In contrast, the PS3 is the console that has the largest loss per manufacturing cost ($50). It makes sense that Sony would keep these two brethren consoles in parallel in order to offset the loss incurred by the other.
There is evidence that the latest iteration of the PS3 has all the hooks in place to play PS2 games. There is even the PS2 saved game tool still intact in XMB within the PS3. It makes perfect sense that at some point Sony will EOL (end of life) the PS2 and start putting up PS2 games on the PSN. This will of course mean that there will be a firmware update with the emulator tucked inside it as well. Till then we just have to be a bit more patient and play them on the PS2.