The backwards compatible feature was taken out due to production costs. Many gamers were pretty upset by it. All systems of all regions were affected.

You can tell the different between the systems is this: 4 USB ports in the front for the controllers. Slim and uber slims are NOT backwards compatible.

So, if you want to find a system that has backwards compatibility, you can expect to pay a hefty price and have many headaches due to the system's rarity. I think the 80g PS3s are rarer than the 60g PS3. Not sure depending on the region you live in.

My suggestion is to do a little research before buying. It can go along way.