This method involves injecting a game into a single game emulator. It's how the Wii "emulated" the GameCube. Or how the PSP does it. If a game is similar enough you can inject a game and it'll run. They don't include it stand alone cause of the testing required. Plus extra cash.

The Wii never emulated the GameCube, the Wii was a GameCube (with higher clock-rates). This has nothing to do with what PS3 does.

This is one of the reasons why i dont understand why the PS4 doesnt have backwards compatibility with the PS3. Certainly Sony has a team of programmers that can create an emulator for PS3 games... Its the way Micosoft did  with the Xbox/X360 aswell.

It's not possible to emulate the PS3 - not with a PS4 and not with a "real" gaming-rig which costs >1000$. You'd need way too much power.

I thought the PS4 was supposed to be super duper powerful. :P

Easy: the PS4 has nowhere near the CPU/GPU power to correctly emulate a PS3. Game profiles are supposed to be fixes for shortcuts taken in the general emulator code, but can't close a big gap.

A very different architecture implies a substantial overhead and we're talking of seven PowerPC cores at 3.2GHz with a complicated memory access plus a customized GPU that is ancient in PC terms, but still not trivial. Look how sketchy PS2 emulation is on PCs: I doubt you can build a generally good PS3 emulator even for high-end computers.

Xbox->360 (or PS2->PS3) was a much bigger computational step, and I am actually surprised to hear that a general purpose PS2 emulator can run that well on a PS3 without substantial ad-hoc tweaks for each title.

@bolded: no, the spes are not ppc-isa, they have their own.

Made a bit of a mess in my editing there... it was supposed to be "seven SPE+ one PowerPC cores"

Emulators are 100% legal.

ROMs obtained off the Internet of copywritten games, however, are not.

But if you're running a game FROM A RETAIL DISC in your emulator, there's absolutely nothing illegal about it. You 100% legally own both the hardware and the software. You can do what you want with it within the confines of your own home.

in many ways it is.  It is in fact techincally legal to have an emulator playing games that you have already bought on a system that you already own.  It is protected by some law about backups and stuff.