Ever heard of something called architectures? x86, x64, Itanium (IA-64) for example. Well, consoles have different architectures too. For example, XBOX360 and PS3 use PowerPC based CPUs. The code (CPU instructions) for games on each console are either encoded inside XEX (XBOX360 executables) or PS3 SELF (PlayStation 3 Signed Executable and Linkable Format) files. There are obviously not directly compatible with x86/x64 CPUs because it does not recognise/support those kinds of instructions. Windows doesn't know what to do with them either because they're not a Windows EXE or DLL.
That is why emulators exist to convert the instruction set from another architecture to another (eg. PowerPC -> x86). This can be a very time consuming process as there are a large amount of instructions to cover. Not to mention developers have to devote their time in optimizing code to take advantage of advanced CPU features like SSE2, SSE3, SSE4 available on new CPUs. This is in order to provide as much execution speed as possible because converting these instructions on-the-fly while a game is running is a time-consuming operation (this would explain why some emulators are extremely slow). Instructions aren't the only thing they need to worry about too, there's also CPU registers and CPU specific features to cover too. CPUs are complex pieces of hardware, you're suggesting from your posts that they are all the same when they're aren't.
Firmware and BIOS is also a major issue. Obtaining a console's firmware or BIOS can be a difficult task because it's often protected to prevent emulators from being created. Even if you somehow did manage to obtain it, you would have to heavily modify it to accept non-standard hardware because let's face it. A PC's hardware is not identical to a console's one. This will require alot of reverse engineering and research to achieve such a feat.
It IS possible to emulate a PS3 or XBOX360 on a PC. The only issue is that it will take an extremely long amount of time to make and probably isn't really worth your time.