THe "install other OS" feature would maybe have been a big deal if it weren't intended for Linux. MacOS may work for that, too, but I've not checked.
No one was buying the PS3 to use it as a linux-based PC, anyway. Backwards compatibility can be fixed by distributing software emulation of PS2/PS1 games, as that's what they'd have to do for all the PSOne classics anyway.
USB slots... you mean the memory card slots? There have to be USB slots (mini-usb yeah, but still usb) to charge the controllers and power PSEye; Sony's not going to force you to buy one of those Energizer or Nyko charge stands.