Wow they do mean something?? I mean I guess they had to but I never could figure it out!The i was because it had a camera, an "eye". And to steal some creed from apple.
The SP stands for Special if I remember correctly.
But this just makes me thinking putting "New" at the front of the name was an even weirder decision. Slim? Mini? Go? Micro? Can't think of any console or handheld revisions which stuck some other word infront of the base name!