Why is that?

The first gen 20gb and 60GB ps3's did not use the emotion engine chip. They worked by software emulation. Sony stopped backwards compatability with the PS3s when the 40gb versions were released. The reason they gave was so that they can focus on ..."new games". I think that's pretty lame on sony's part since they used software emulation, they could have just as easily left the feature for users. It's probably something they've done to save a few bob.

But tbh, although I have a backwards compatible ps3. I never actually play my PS1/PS2 games, because they are really crap in comparison. Sometimes it is good if you get the urge to play one of the classics... but otherwise they just lay there piling dust.

I disagree. The new games that are coming out for the new platforms aren't THAT good. I'm actually quite disappointed in them, that's why I'm not buying PS3 now.
But it's a shame that the new PS3 won't the backwards compatibility, that means I can't throw out my PS2 when I'll buy the PS3.

If you seriously want to play ps2 games, then buy the first gen ones from eBay. But you will find the 60gb versions sell for a bit more as they are no longer in production and they are in high demand.