Well, I think Sony figured out they could get away with not including it this gen and will probably repeat that next gen as well. Personally, I think it was a mistake for sony to remove backwards compatibility, because it freed up all those ps2 owners to buy a 360 instead if they wanted to.
The reason why I think Sony is going to forgo the backwards compatibility next gen is the cell processor. No way is Sony going to repeat the development discrepancy between platforms again. They are going to go with something easier to program for. Without the cell, it will be impossible to backwards compatibility, at least from a hardware perspective. They could go the 360 route and do software emulation, but it was difficult to do that with xbox games, I can only imagine how much more difficult it would be for ps3 games....