There is a lot of confusion out there about the PS3 and its backwards compatibility. The short answer is that there are MULTIPLE versions of the PS3 in production and some are backwards compatible - while others are not.
For example, in our household we have two PS3 units. One of them, bought the very first day of release, IS backwards compatible. It can play PS2 games. Another one, bought in the fall of 2008, is NOT backwards compatible. It can NOT play PS2 games.
There are no set rules. It is not that "every single 60 gig PS3 ever made is backwards compatible". You have to look at the specs of the MACHINE YOU ARE INTENDING ON BUYING to see if it says if it is backwards compatible or not.
So really, the question is why you would "give up" backwards compatibility? Why would you deliberately buy one of the newer machines that is not backwards compatible?
The answer comes down to system reliability, heat and noise. When they first launched the PS3, they were all backwards compatible by default. In order to make this system be able to play both new high-end games and old low-end games, they had to have a lot more processor and code in the PS3 unit. It makes sense - it had to in essence be two gaming systems at once. This meant the system was a HUGE energy drain. It also meant the system heated up like crazy, to maintain all of that hardware. Which then also meant the fan had to run a lot, to try to keep the system from melting down. Which then also meant the system had failures, because of all of that heat.
Over time a lot of people in the PS3 community said they would MUCH rather have a system which only ran PS3 games, and ran them well. They used their PS3s for BluRay DVD players, which is awesome and they wanted a quiet system. Nobody wants to be watching an incredible movie and have the dialogue drowned out by the fan noise!
So because of all of this, Sony came out with a new set of PS3s that were NOT backwards compatible. These new systems only played PS3 games. Because they did not have all that "baggage" of trying to also handle PS2 games, they run much more quietly. They are literally whisper-quiet. They draw a lot less energy, so they don't heat up. So they are much more long-term reliable. They are cheaper to run! So this is all around a superb solution.
Yes, we have PS2 games in the house. We have a PS2 to play them! There's no reason for us to gum up our PS3 with those PS2 games. PS2 units are cheap.
So if you enjoy PS2 games, I definitely recommend keeping a PS2 around to play them - but get a PS3 that is NOT backwards compatible. Your pocketbook will thank you because of the cheaper electrical bill, you will have a PS3 that lasts much longer, and when you watch movies you will enjoy the experience. It's an all around win situation.