No hope in the world of them restoring PS2 compatibility I reckon... all done to reduce price, hence the new version slimline PS3.
I suspect that they've probably moved the power unit to an external one and therefore also saved component costs on the need to have a cooling fan as well.
Smaller form factor and different disc loading mechanism are also new additions to cut production costs.
Up until now, you could have a 360 and a Wii for the same price as a PS3, so of course Sony had to do something about it.
I have both the 360 and the PS3, and I must say that the Xbox gets used for games more whereas the PS3 is an expensive living room ornament/back up Blu-ray player.
Get the PS3 if you want to get into hi-def Blu-ray movies but otherwise, the 360 is fine if you only want to play games.