Yeah and right now, we can only accurately emulate up to Nintendo 64 era. Playstation 1 emulation is pretty choppy, and even N64 has its quirks, but for the most part it's good for N64/Playstation 1 and everything before that is fine. Handhelds are also easier to emulate due to the less powerful hardware.
So maybe in 10 years you could emulate Xbox 360/PS3, but even now Gamecube emulators run at like 3 fps.