The transfer fee above 1-2 monetary units... No thanks.
The transfer free... There it's obvious why that won't happen.
"Hey dude, can I borrow your PSP stuff for the weekend?"
Wash... Repeat...
Charging $5+ to transfer isn't ethically "bad" either, it's just insulting, bad.
Nintendo is a different case. Gamecube works on Wii (up to recently - MiniWii: Successor to NES-Topper and SNES2). DS works on 3DS. That's full BC. VC is a cherry and optional. Going back 2 steps (or more), even though that's all Sony has at this time... Meh. It adds little value to a PS3 over a PS2. The PS2 is arguably still a better platform because you have the entire PS1/2 library at your disposal for $30-$80 entry fee. Vita can't go BC back one, let alone two. UMD was error, and not forward thinking. Sony will still take the UMD hit through the Vita cycle. Just this time, a glancing blow.
Also remember, Sony was responsible for consumer expectation of BC... They're getting better, but they're still rather schizo and narcissistic.