Dolphin has support for two consoles: Gamecube and Wii. It supports both of them because the architectures are extremely similar. I don't get what you mean by "ease of programming model". Saturn/Playstation/N64 were the first to have games programmed primarily in C with libraries provided by the system developers. This generation is harder to emulate simply because the system architectures contain more chips connected with wider buses running at much higher clock speeds. All of those factors make low level analysis, like with a logic analyzer, impractical. Another factor is the popularity of the system and level of interest in emulation of the system. The original XBox is a good example of this. Gamecube and PS2 have much more polished emulators because they have more titles that interest people, while little effort is spent on emulating the original Xbox (despite being essentially a PC) arguably due to the lack of exclusive titles to make it worth it.