SACD was hardware. In order to actually handle reading the variable pit length scheme (Pit Signal Processing), the drive itself had additional hardware. This isn't the same as decoding DSD streams, this is part of the reason why while SACDs are basically DVDs, your average DVD drive cannot actually decrypt the data on the disc.
PS2 backcompat was also hardware. The Emotion Engine *and* the Graphics Synthesizer chip were both included on the launch PS3 with software handling the rest of the system, such as the IOP (which is why PSX emulation is done entirely in software). The next revision had the EE cut, but the GS chip itself still remained. Now there's absolutely no PS2 hardware in the system.
These are cost-cutting methods, however, it's a total misnomer to actually claim this is just flipping some software bits like removing Other OS support has been.