The PS3 firmware has embedded PS2, PS1 and PSP emulators.Ok, lets look at the ps3. I have loaded PS2 backups with multiman on my slim. I'm sure that not all ps2 backups will work, but the 6 or 7 games that I did try worked fine. The 3DS scene needs to progress, cfw is still kind of new. The method that Nintendo uses to launch a gamecube and wii titles on the 3DS needs to be more thoroughly examined. Don't say that it isn't possible because somebody will prove you wrong.
When you run your backups through it the manager simply calls those emulators and gave them the backup location so it can load them.
While the PS3 itself doesn't have all the hardware that those older systems used, it's hardware is powerful enough and Sony engineers know how to program a emulator with the proper speedhacks to achieve playable end results (it's in no way a proper 1:1 emulation, they use lots of tricks to achieve similar results with less resource).
Nintendo doesn't launch/emulate Wii or GC games on 3DS, you can run games with similar graphics and physics through porting* the games. If you bring good artists along you can redo the graphical assets to be better looking on 3DS small screens and resolutions.
* To port a game is to get their original source code, optimize it to the new target system and then recompile and sell this. It's completely different and unrelated to emulation.