No worries - it's just that most emulators do things differently to try and make things work. Emulating even that simple of a system exactly as it was designed is actually quite difficult (partially because the hardware in a gaming console is usually very specialized and customized, and partially because making a different processor architecture emulate something that custom requires either a LOT of horsepower, or emulation tricks to avoid certain issues). You either have something that runs with decent speed but doesn't exactly emulate the original environment and has bugs (which can cause issues in the games that then run in the emulator), or you emulate the original hardware perfectly, bug for bug, and you end up with something that's much more difficult for the non-like hardware doing the emulation to achieve.
For example, Nestopia is probably the most accurate emulator available to the original NES design, and requires anywhere from 800MHz to 1.5-1.6GHz of Intel x86 CPU power to properly emulate the equivalent of a TI graphing calculator. The developer of this has moved to SNES emulation (again, as close to the original as possible), and has found that he needs 3+GHz on an Intel platform to approach being proper emulation of the SNES hardware. That gaming console hardware was from 1990, and had hardware for CPU and audio that ran at ~21MHz. Again, the issue isn't speed, it's timing and accuracy - that hardware, while paltry in speed, was highly optimized to do what that device did. Emulating something from 1990 at about 21MHz takes upwards of 3GHz on today's hardware.... Interesting, no?